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DYNAMICS OF DISEASE DYNAMICS OF DISEASE TRANSMISSIONTRANSMISSION
Dr Sanat RathodAssistant Professor
GMERS Medical CollegeGotri
Vadodara
22
1st - The Infectious Agent1st - The Infectious Agent
3
-any disease-causing -any disease-causing microorganism microorganism (pathogen)(pathogen)
InfectivityInfectivity
PathogenicityPathogenicity
Virulence Virulence
2nd Source or Reservoirbull The starting point for the occurrence of a communicable disease
bull Source of infection Source of infection bull the person animal object or substance from which an the person animal object or substance from which an
infectious agent passes or is disseminated to the host infectious agent passes or is disseminated to the host (immediate source)(immediate source)
bull RESERVOIRRESERVOIR bull ldquoldquoany person animal arthropod plant soil or any person animal arthropod plant soil or
substance or a combination of these in which an substance or a combination of these in which an infectious agent normally infectious agent normally lives and multiplieslives and multiplies on on which it which it depends primarily for survivaldepends primarily for survival and where it and where it reproduces reproduces itself in such a manner that it can be itself in such a manner that it can be transmitted to a susceptible host transmitted to a susceptible host It is the natural habitat of the infectious agentrdquo It is the natural habitat of the infectious agentrdquo
4
bull5
Types of Reservoirs
Human reservoir
Animalreservoir
Non-livingreservoir
6
cases carrierscarriers
bullClinical cases (mildsevere-typicalatypical)bullSub-clinical casesbullLatent infection cases
bullPrimary casebullIndex casebullSecondary cases
TypebullIncubatorybullConvalescentbullhealthy
DurationbullTemporarybullChronic
Portal of exitbullUrinarybullIntestinalbullRespiratorybullothers
ldquoA person in the population or study group Identified as having particular disease health disorder or condition
Under investigationrdquo
7
The clinical illness maybe mild or moderate typical or atypical severe or fatal
Epidemiologically mild cases may be more important sources of infection than severe cases because they are ambulant and spread the infection wherever they go whereas severe cases usually confined to bed
8
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
22
1st - The Infectious Agent1st - The Infectious Agent
3
-any disease-causing -any disease-causing microorganism microorganism (pathogen)(pathogen)
InfectivityInfectivity
PathogenicityPathogenicity
Virulence Virulence
2nd Source or Reservoirbull The starting point for the occurrence of a communicable disease
bull Source of infection Source of infection bull the person animal object or substance from which an the person animal object or substance from which an
infectious agent passes or is disseminated to the host infectious agent passes or is disseminated to the host (immediate source)(immediate source)
bull RESERVOIRRESERVOIR bull ldquoldquoany person animal arthropod plant soil or any person animal arthropod plant soil or
substance or a combination of these in which an substance or a combination of these in which an infectious agent normally infectious agent normally lives and multiplieslives and multiplies on on which it which it depends primarily for survivaldepends primarily for survival and where it and where it reproduces reproduces itself in such a manner that it can be itself in such a manner that it can be transmitted to a susceptible host transmitted to a susceptible host It is the natural habitat of the infectious agentrdquo It is the natural habitat of the infectious agentrdquo
4
bull5
Types of Reservoirs
Human reservoir
Animalreservoir
Non-livingreservoir
6
cases carrierscarriers
bullClinical cases (mildsevere-typicalatypical)bullSub-clinical casesbullLatent infection cases
bullPrimary casebullIndex casebullSecondary cases
TypebullIncubatorybullConvalescentbullhealthy
DurationbullTemporarybullChronic
Portal of exitbullUrinarybullIntestinalbullRespiratorybullothers
ldquoA person in the population or study group Identified as having particular disease health disorder or condition
Under investigationrdquo
7
The clinical illness maybe mild or moderate typical or atypical severe or fatal
Epidemiologically mild cases may be more important sources of infection than severe cases because they are ambulant and spread the infection wherever they go whereas severe cases usually confined to bed
8
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
1st - The Infectious Agent1st - The Infectious Agent
3
-any disease-causing -any disease-causing microorganism microorganism (pathogen)(pathogen)
InfectivityInfectivity
PathogenicityPathogenicity
Virulence Virulence
2nd Source or Reservoirbull The starting point for the occurrence of a communicable disease
bull Source of infection Source of infection bull the person animal object or substance from which an the person animal object or substance from which an
infectious agent passes or is disseminated to the host infectious agent passes or is disseminated to the host (immediate source)(immediate source)
bull RESERVOIRRESERVOIR bull ldquoldquoany person animal arthropod plant soil or any person animal arthropod plant soil or
substance or a combination of these in which an substance or a combination of these in which an infectious agent normally infectious agent normally lives and multiplieslives and multiplies on on which it which it depends primarily for survivaldepends primarily for survival and where it and where it reproduces reproduces itself in such a manner that it can be itself in such a manner that it can be transmitted to a susceptible host transmitted to a susceptible host It is the natural habitat of the infectious agentrdquo It is the natural habitat of the infectious agentrdquo
4
bull5
Types of Reservoirs
Human reservoir
Animalreservoir
Non-livingreservoir
6
cases carrierscarriers
bullClinical cases (mildsevere-typicalatypical)bullSub-clinical casesbullLatent infection cases
bullPrimary casebullIndex casebullSecondary cases
TypebullIncubatorybullConvalescentbullhealthy
DurationbullTemporarybullChronic
Portal of exitbullUrinarybullIntestinalbullRespiratorybullothers
ldquoA person in the population or study group Identified as having particular disease health disorder or condition
Under investigationrdquo
7
The clinical illness maybe mild or moderate typical or atypical severe or fatal
Epidemiologically mild cases may be more important sources of infection than severe cases because they are ambulant and spread the infection wherever they go whereas severe cases usually confined to bed
8
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
2nd Source or Reservoirbull The starting point for the occurrence of a communicable disease
bull Source of infection Source of infection bull the person animal object or substance from which an the person animal object or substance from which an
infectious agent passes or is disseminated to the host infectious agent passes or is disseminated to the host (immediate source)(immediate source)
bull RESERVOIRRESERVOIR bull ldquoldquoany person animal arthropod plant soil or any person animal arthropod plant soil or
substance or a combination of these in which an substance or a combination of these in which an infectious agent normally infectious agent normally lives and multiplieslives and multiplies on on which it which it depends primarily for survivaldepends primarily for survival and where it and where it reproduces reproduces itself in such a manner that it can be itself in such a manner that it can be transmitted to a susceptible host transmitted to a susceptible host It is the natural habitat of the infectious agentrdquo It is the natural habitat of the infectious agentrdquo
4
bull5
Types of Reservoirs
Human reservoir
Animalreservoir
Non-livingreservoir
6
cases carrierscarriers
bullClinical cases (mildsevere-typicalatypical)bullSub-clinical casesbullLatent infection cases
bullPrimary casebullIndex casebullSecondary cases
TypebullIncubatorybullConvalescentbullhealthy
DurationbullTemporarybullChronic
Portal of exitbullUrinarybullIntestinalbullRespiratorybullothers
ldquoA person in the population or study group Identified as having particular disease health disorder or condition
Under investigationrdquo
7
The clinical illness maybe mild or moderate typical or atypical severe or fatal
Epidemiologically mild cases may be more important sources of infection than severe cases because they are ambulant and spread the infection wherever they go whereas severe cases usually confined to bed
8
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
bull5
Types of Reservoirs
Human reservoir
Animalreservoir
Non-livingreservoir
6
cases carrierscarriers
bullClinical cases (mildsevere-typicalatypical)bullSub-clinical casesbullLatent infection cases
bullPrimary casebullIndex casebullSecondary cases
TypebullIncubatorybullConvalescentbullhealthy
DurationbullTemporarybullChronic
Portal of exitbullUrinarybullIntestinalbullRespiratorybullothers
ldquoA person in the population or study group Identified as having particular disease health disorder or condition
Under investigationrdquo
7
The clinical illness maybe mild or moderate typical or atypical severe or fatal
Epidemiologically mild cases may be more important sources of infection than severe cases because they are ambulant and spread the infection wherever they go whereas severe cases usually confined to bed
8
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
6
cases carrierscarriers
bullClinical cases (mildsevere-typicalatypical)bullSub-clinical casesbullLatent infection cases
bullPrimary casebullIndex casebullSecondary cases
TypebullIncubatorybullConvalescentbullhealthy
DurationbullTemporarybullChronic
Portal of exitbullUrinarybullIntestinalbullRespiratorybullothers
ldquoA person in the population or study group Identified as having particular disease health disorder or condition
Under investigationrdquo
7
The clinical illness maybe mild or moderate typical or atypical severe or fatal
Epidemiologically mild cases may be more important sources of infection than severe cases because they are ambulant and spread the infection wherever they go whereas severe cases usually confined to bed
8
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
ldquoA person in the population or study group Identified as having particular disease health disorder or condition
Under investigationrdquo
7
The clinical illness maybe mild or moderate typical or atypical severe or fatal
Epidemiologically mild cases may be more important sources of infection than severe cases because they are ambulant and spread the infection wherever they go whereas severe cases usually confined to bed
8
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
The clinical illness maybe mild or moderate typical or atypical severe or fatal
Epidemiologically mild cases may be more important sources of infection than severe cases because they are ambulant and spread the infection wherever they go whereas severe cases usually confined to bed
8
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Subclinical casesSubclinical cases
Inapparent Covert Missed or Abortive CasesInapparent Covert Missed or Abortive Cases
bull disease agent multiplymultiply in the host but does not manifest by SS
bull But contaminates the environment in the same way as clinical cases
bull Subclinical cases play a dominant role in maintaining the chain of infection in the community
9
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
subclinical casesdetected only detected only
by by laboratory laboratory teststests
occurs in most infectious disease
Eg Rubella Mumps Polio Hepatitis A and B Influenza Diphtheria 10
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Latent infectionbull infectious agent lies in ain a non-infectious non-infectious form-form-dormantdormant within the host without symptomssymptoms
with no shedding shedding (and often without demonstrable presence in blood tissues or bodily secretions of the host)
eg eg HSV and VZV nerve ganglia cells
CMV kidney and salivary glands cells EBV lymphocytes
11
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Index Case Person that comes to the
attention of public health authorities
Primary Case First case of a communicable
disease introduced into the population unit bring studied
Attack rate
Secondary Case Person who acquires the
disease from an exposure to the primary case
Secondary attack rate12
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
CarriersCarriers An An infected person or animal infected person or animal that that harborsharbors a a specific infectious agent in the specific infectious agent in the absence absence of of discernible (visible) clinical disease and serves discernible (visible) clinical disease and serves as a as a potential source potential source of infection to othersof infection to others
13
Reason
due to inadequate treatment or immune response
the disease agent is not completely eliminated
leading to a carrier state
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Three elements in a carrier Three elements in a carrier statestate
14
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
CARRIERSCARRIERS
As a rule carriers are less infectious As a rule carriers are less infectious than cases but epidemiologically than cases but epidemiologically they are more dangerous than cases they are more dangerous than cases
because escape recognition continuing to live a normal life among
population or community readily infect the susceptible individuals over a wider area and longer period of
time under favorable conditions
15
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Incubatory Carriers Incubatory Carriers those who shed the
infectious agent during the incubation period This usually occurs during last few days of IP
Measles- the period of communicability is 4 days before the rash
Mumps- usually 4-6 days before onset of symptoms Polio- 7-10 days before onset of symptoms Hepatitis B- for a month before jaundice Pertusis Influenza Diphtheria
16
Classification of Carrier Classification of Carrier
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Carrier May Be Classified Carrier May Be Classified By TypeBy Type
Convalescent Carriers Convalescent Carriers
those who continue to shed the disease agent during the period of convalescence
In the disease clinical recovery does not coincide with bacteriological recovery
Serious threat to HH members Highlights importance of bacteriological
surveillance of carriere state after recovery
typhoid fever cholera diphtheria bacillary dysentery pertusis
17
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Carrier may be classified Carrier may be classified BY TYPEBY TYPE
Healthy Carriers Healthy Carriers victims of subclinical infection who have
developed carrier state without suffering from overt disease but are nevertheless shedding the disease agent
poliomyelitis cholera meningococcal meningitis salmonellosis diphtheria
18
Note- Person whose infection remains subclinical may or may not act as carrier (eg- in polio inf may remain subclinical but person act as temp carrier due to shedding of virus in stoolwhile TB most of us with +ve Mt do not disseminate bacillie- so not labelled as carrier
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Temporary carriers Temporary carriers are those who shed the infectious agent for short period of time
Chronic carriers Chronic carriers are those who excretes the infectious agent for indefinite periods
19
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Chronic carriersChronic carriersChronic carriers are far more important
sources of infection than cases The longer the carrier state the greater the
risk of community-- reintroduce disease into areas which are otherwise free of infection
The duration of the carrier state varies with the disease In typhoid fever and hepatitis B the
chronic carrier state may last for several years
In chronic dysentery it may last for year or longer
In diphtheria the carrier state is associated with infected tonsils in typhoid fever with gall bladder disease
20
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Mary Mallon (1869 ndash1938) better known as Typhoid Mary was the first person in the US identified as an asymptomatic carrier of the pathogen associated with typhoid fever
She was presumed to have infected some 50 people three of whom died over the course of her career as a cook
She was forcibly isolated twice by public health authorities and died after a total of nearly three decades in isolation
21
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Respiratory carrier eg influenza
Fecal (intestinal) carrier eg typhoid
cholera
Blood carrier eg hepatitis B and HIV
Urinary eg Typhoid
sexual Carrier gonococcus and HIV
22
Carrier classified Carrier classified By Portal Of Exit of Infectious Agent
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Animal reservoirsAnimal reservoirs
bull infection that is transmissible under natural conditions from animals to man
bull eg ndash Bacterial Leptospira plague from Ratndash Viral Rabies from dogndash Protozoa Leishmaniasis from dogndash Helminths Hydatid disease from dog ndash Tape worms Cattle Pig
bull23
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Reservoir in non-living Reservoir in non-living thingsthings
Some organisms are able to Some organisms are able to survive and multiply in survive and multiply in nonliving environments nonliving environments such as soil and watersuch as soil and water
Clostridium that causes tetanus Clostridium that causes tetanus and botulism can survive many and botulism can survive many years in the soilyears in the soil
Hookworms deposit their eggs Hookworms deposit their eggs into the soilinto the soil
Water contaminated by human Water contaminated by human or animal feces cause GI tract or animal feces cause GI tract disease (list includes bacteria disease (list includes bacteria viruses protozoa)viruses protozoa)
bull24
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
3rd - The Portal of Exit3rd - The Portal of Exit
25
bull Route of escape of the pathogen Route of escape of the pathogen from the reservoirfrom the reservoir-IA enters into surrounding env-transfer to host at their portal of entryExamples
respiratory secretions respiratory secretions
GIGI
blood exposureblood exposure
breaks in skinbreaks in skin
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
4th ndashMode of Transmission4th ndashMode of Transmission
26
Direct transmission
Indirecttransmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
vertical
Vehicle-borne
bullVector-borne
Air-borne
Fomite-born
Unclean hands and fingers
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Direct TransmissionDirect Transmission
bull27
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Direct ContactbullInf spread by direct contact of skin-skin skin mucosa mucosa-mucosa of same or other personbullby touching kissing by touching kissing bites or sexual intercoursebites or sexual intercourse
bullDirect amp immediate transfer of IA from reserviour ndashhost (no intermediate agency)
bullSo it introduces larger dose of IA bullNo time interval of survival in environment
bullOvercrowded place or where place with lack of ventilation
bull28
ScabiesPediculosis
STDrsquosSkineye inf
leprosy
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Droplet spread Droplet spread bull Direct projection of Direct projection of
droplets of droplets of
salivanasopharyngsalivanasopharyng
eal secretion by eal secretion by
Sneezing Sneezing
Speaking Speaking
Coughing Coughing
bull Droplets directly Droplets directly
impinge on impinge on
conjunctiva nasal conjunctiva nasal
mucosa or skinmucosa or skin
bull29
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
bull30
bull H1N1H1N1bull Tubercle bacilliTubercle bacillibull MeaslesMeaslesbull ChickenpoxChickenpox
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
bull InoculationPathogen injected into tissues
ndash Tetanus sporesndash Arboviruses (Insects)
bull31
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Vertical transmissionVertical transmission
Transplacental Transplacental
To R C H To R C H HIVHIV HBVHBV
bull3215
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Indirect Transmission
5 lsquoFrsquo
33food flies fomite finger fluid
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Vehicle transmission
bull Water Cholera H A V H E V Typhoid etc
bull FOOD FOOD Staphylococci Cl Botulinum
bull Bloodserum-HIV HBVHCVbull Organ-cmv
34
Clustering of casesClustering of cases Distance bw secondary cases Distance bw secondary cases
moremore Common source can be tracedCommon source can be traced
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
MechanicalHf
DiarrheaDysenteryTyphoid
Trachoma
BiologicalBiological
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
PropagativeOnly multiplicationNo developmental
Plague bacilli in rat flea
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
Cyclo propagativeMultiplicationdevelopmental
Malaria parasites in mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
CyclodevelopmentalNo multiplication developmentalFilaria parasite
In mosquito
Vector-insects
35
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Trans-ovarian transmission Inf agent vertical transmitted from
female mosquito to her progeny Scrub typhus Rickettsial pox Indian tick typhus Q fever RMSF
Trans-stadial transmission-Trans-stadial transmission- Lyme disease infects tick vector as a larva
and the infection is maintained when it molts to a nymph and later develops as an adult
36
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
host feeding preference infectivity-ability to transmit disease agent susceptibility ndash ability to become infected survival rate of vectors in environment Domesticity Seasonal factorshellip
37
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
FomitesFomites
Contaminated Contaminated Nonliving Objects Nonliving Objects like Cup towel
napkin linen Clothing glass Toys Pencils door
handle surgical instruments syringes dressing
materialshellip
Ex Diphtheria
Trachoma
influenza
scabies 38
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
5th - The Portal of Entry5th - The Portal of Entry
bull39
-route through which -route through which the pathogen enters its the pathogen enters its new hostnew host
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Respiratory System
inhal
atio
inhal
atio
nn
bull40
Upper respiratory tract Diphtheria
Lower respiratory tract Tuberculosis
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Gastrointestinal System
ing
esti
on
ing
esti
on
FecFeco-o-Oral RouteOral Route
Infectious agent excreted in faeces amp transmitted to the oralportal of entry through1048707 contaminated food water milk drinks1048707 hands
bull1048698 Typhoid feverbull1048698 Shigellabull1048698 Cholerabull1048698 Poliobull1048698 Rotavirusbull1048698 Hepatitis A Hepatitis E
bull41
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Urinary amp Reproductive Tracts
Sexu
al
Sexu
al
cont
act
cont
act
bull42
GonorrheaSyphilisHIV
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Breaks in Protective Skin Barrier
bull43
Percutaneous
Leptospirosis
Percutaneous (bite of arthropod) Yellow fever
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
6th - The6th - The Susceptible HostSusceptible Host
44
A person or an animal that afford A person or an animal that afford lodgment to an infectious agent lodgment to an infectious agent under natural conditions under natural conditions
bullAccepts the pathogen
bullThe support of pathogen life amp its reproduction depend on the degree of the hostrsquos resistance
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
bullCancer Patients
bullHIV-AIDS Patients
bullTransplant Patients
bullOn steroids
bullInfant amp Elderly Patients
45
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
HOSTHOST
Obligate hosObligate host the only host
Eg Man in measles amp typhoid
Primary definitive Primary definitive host in which parasite attains maturity or passes its sexual stage
Secondary or intermediate Secondary or intermediate hosts the parasite is in a larval or asexual state
bull46
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Life cycle Sporozoits Liver
Ring Trophozoits
Marozoits
RBC
Mature
Schizont
Mature
Gametocyte
Male FemaleMosquitoZygote
Ookinete
Oocyte
Salivary Gland
Exflagellation
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
THE TIME INTERVAL BETWEEN INVASION BY AN INFECTIOUS AGENT AND APPEARANCE OF
THE FIRST SIGN OR SYMPTOM OF THE DISEASE IN QUESTION
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
DOSE OF INOCULUMSITE OF MULTIFICATIONRATE OF MULTIFICATIONHOST DEFENCE MECHANISM
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
0
5
10
15
Time
1 Median onset time
23
50 50Probable exposure time
Median incubation timeNo of cases
1 2 3 4 5 6 7 8 9 1011 12 1314 1516 171819 20 21 22
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Period From Disease Initiation To Period From Disease Initiation To Disease DetectionDisease Detection
For NCDs For NCDs
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
0
5
10
Zeit
No of cases
Generation
time
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
GENERATION TIMEGENERATION TIME
INTERVAL OF TIME BETWEEN RECEIPT OF INTERVAL OF TIME BETWEEN RECEIPT OF INFECTION BY A HOST AND MAXIMAL INFECTION BY A HOST AND MAXIMAL
INFECTIVITY OF THAT HOSTINFECTIVITY OF THAT HOST
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
THE GAP IN TIME BETWEEN THE ONSET OF THE PRIMARY CASE AND THE SECONDARY CASE
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
It is defined as the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person from an infected animal to man or from an infected person to an animal including arthropods
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
6411477613310
Attack Rate
TotalWellIllAttack Rate
TotalWellIll
Did not eat the food (not exposed)Ate the food (exposed)
Attack Rate = Ill (Ill + Well) x 100 during a time period
Attack rate = (1013) x 100 = 76 ( 711) x 100 = 64
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
It is defined as the number of exposed It is defined as the number of exposed persons developing the disease within the persons developing the disease within the range of the incubation period following range of the incubation period following exposure to the primary caseexposure to the primary case
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Used to estimate to the spread of disease in Used to estimate to the spread of disease in
a family household or other group a family household or other group
environmentenvironment Measures the infectivity of the agent and the Measures the infectivity of the agent and the
effects of prophylactic agents (eg vaccine)effects of prophylactic agents (eg vaccine)
58
SAR ()Total number of cases ndash initial case(s)
Number of susceptible persons in the group ndash initial case(s)
= x 100
Thank YouThank You
Thank YouThank You
![Infection control disease transmission([1]](https://img.dokumen.tips/doc/110x75/54838305b4af9fd8678b46d0/infection-control-disease-transmission1.jpg)
