Infectious Disease Epidemiology, Module I
Introduction
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Introduction Round table Your expectations of this day Your career goals Knowledge base Why is infectious disease epidemiology
important?
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General goals Understand the infectious disease
process Identify transmission routes, modes,
media and reservoirs Understand public health law
Understand infectious disease surveillance Understand the process of outbreak
investigation
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What causes disease?
AgentAgent HostHost
EnvironmentEnvironment
BacteriaBacteriaVirusesVirusesFungiFungiParasiteParasitessPrionsPrions
HousingHousing FoodFoodWater qualityWater quality Air qualityAir quality
AgeAgeGenderGenderEthnic groupEthnic groupLifestyleLifestyleSocioeconomicSocioeconomic
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Expos
ureIn
fect
ion
Diseas
e, sy
mpto
mat
ic/
asym
ptom
atic
Carrie
r
Conva
lesce
nt
Sequela
e
Infectious disease process
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What determines infection?
(other than exposure) The deposition, colonisation and
multiplication of an organism in a host, Usually accompanied by an immune
response May occur with or without clinical illness
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Predictors of infectionAGENT
HOST ENVIRONMENT
ImmunityRaceAge
Gender
Socioeconomic
Living Conditions
Social
Climate
Dose
Genetics
Hardiness
Communicability
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Infectious disease process - Source
Reservoirs human insect animal
Medium air borne water borne food borne blood borne genital
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Infectious disease process- Transmission
Route direct
Oral, oral/faecal sexual respiratory - droplets or droplet nuclei 1-5m parenteral congenital
indirect vector vehicle
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Infectious disease process -Infection & Incubation
Infection dose infectivity hardiness rate of replication
Incubation infectiousness immune response intervention
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Infectious disease process- Disease
Disease signs, symptoms asymptomatic infectious
Outcome/Prognosis morbidity mortality sequelae recovery
infectious (chronic carrier)
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Diagnosis Clinical
based on signs, symptoms Laboratory confirmed
microbiology detection isolation
serology parasitology virus
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Diagnostic process
Patient presents due to symptoms case - finding
screening active investigation of contacts
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Laboratory diagnosis
Lab tests ordered Method of collection, site, volume Right tests ordered
correct organisms antimicrobial sensitivity
Sent to the right place In the right media Transport conditions
Time Temperature
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Laboratory diagnosis, (cont.) Routine identification of organisms causing
diarrhoea C & S
shigellae salmonellae yersinia aeromonas campylobacter
In children < 5 in the summer Vertoxigenic E. coli
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Laboratory diagnosis, (cont.)
If food-borne is suspected and written on the requisition staph aureus bacillus cereus clostridium perfringens
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Interpretation of tests, if positive
Test sensitivity % of people accurately diagnosed as ill of all
people tested Normal flora?
N. meningitidis Streptococcus pyogenes
Carrier state Contamination during collection Lab. Error Multiple infections
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Interpretation of tests, if negative
Prior antibiotic therapy Problems in
collection timing site
storage transport media
Failure to incubate long enough
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Summary
Infectious disease process reservoir - transmission - disease/death
Determinants of infection agent, host, environment interaction
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Next Steps Future applied
disease in populations surveillance outbreaks