Prof. Saman Wimalasundera

MBBS DO PhDMBBS DO PhDProfessor in Community MedicineProfessor in Community Medicine

Former Head, Department of Former Head, Department of Community MedicineCommunity Medicine

In charge OphthalmologistIn charge OphthalmologistCommunity Ophthalmology centerCommunity Ophthalmology center

Faculty of MedicineFaculty of MedicineUniversity of RuhunaUniversity of Ruhuna

Galle Galle Sri LankaSri Lanka

Epidemiology and

its application

The concepts of epidemiology were first suggested by Hippocrates in the fifth century B.C. that the development of human disease might be related to external and personnel environment of an individual.

The word epidemiology is derived from Greek and means “Studies upon people”

Epi – Upon, Demos – People, Logia – Study

In contrast to clinical medicine epidemiology involves the study of group of people ratherthan individuals.

Epidemiologist vs. Epidemiologist vs. clinicianclinician

A clinician identifies the ailment in his patients using certain scientifically developed tools to ascertain history of illness, clinical examinationand investigations.

Epidemiologist addresses the understanding of the distribution and determinants of a disease in a community (not an individual) using standard parameters.

What constitute What constitute epidemiologyepidemiology

Epidemiology includes:-

1. The methods for measuring the health ofgroups and determining the attributes and exposures that influence health.

2. The study of the occurrence of disease in its natural habitat rather than in the controlled environment of the laboratory.

3. The methods for the quantitative study of the distribution, variation, and determinantsof health related outcomes in specific groups (sub populations) of individuals, andthe application of this study to the diagnosis, treatment, and prevention of disease status or events.

Evolution of epidemiologyEvolution of epidemiology

The evolution of medical sciences in its earlier phase was based on curative medicine. The primary objective was to cure a patient of his illness. Doctors in historicaltimes looked at their patients as ill people who needed some treatment.

Thus medical science was individual oriented. But gradually it became evident that better human health could be achievedby prevention of diseases rather than by cure.

A Historical Sketch A Historical Sketch

A Long sketch of time ran for more than 2 millennia from Hippocrates (470-400 B.C.) to the first third of 19th century.

Hippocrates developed the medical approach by providing concise, accurate and complete description of actual clinical cases.

An Italian clinician called Bernardino Ramazzini in 1700 moved from observation ofclinical cases to the consideration of ‘workcircumstances’ in similar cases. He is now regarded as the founder of occupational medicine. (Explained in his book. “De Morbis Artificum Diatriba”).

The major step forward in epidemiology occurred in 1662. John Graunt analyzed the weekly reports of births and deaths in London.

For the first time in the history, a quantified pattern of disease, deaths and births was Found. John Graunt is regarded as the founder of demography now.

His observations were published in his book. Named “ the nature and political observations made upon the bills of Mortality”.

After two centuries William Farr (1839) a physician was given the responsibility for medical statistics in England and Wales. Heset up a system for routine compilation of vital statistics and application of data for evaluationof deaths.

Hippocrates, Ramzinni, Graunt and Farr contributed to the understanding of diseasefrequency and distribution.

Another British physician John Snow formulated and tested a hypothesis concerningthe origins of an epidemic of cholera in Londonon the basis of available descriptive data.

Snow postulated that cholera was transmitted by contaminated water. (then unknown mechanism)

He observed that death rates from Cholera were particularly high in certain areas of London.

Those areas were supplied with water by two water companies namely “Lambeth” and “Southwark & Vauxhall” in 1849. Both the companies that time drew water from riverThemes at a point heavily polluted with sewage.

The Lambeth company then changed its source to an area of Themes where the waterwas quite free from sewage of London.

The rate of cholera deaths then declined in those areas suppied by Lambeth company.

Water company Population in 1851

Cholera deaths in 1853-1854

Deaths per 100,000 living

Southwark and Vauxhall

Both companies

Lambeth

167, 654

301, 149

14, 632

192

182

00

114

60

00

Death rates from choleraDeath rates from choleraAccording to water company supplying sub districts of London

Concepts of epidemiology Concepts of epidemiology Definitions

“Epidemiology is defined as the study of the distribution and determinants of health related status or events in specified populations and the application of this study to control the health problems” (Last 1988)

Applications of epidemiologyApplications of epidemiologyThe epidemiology is useful in:

1. Search of cause/causes of disease/diseases.

2. Helps to describe the health status of population or groups.

3. Helps to discover and bridge gaps in natural history of diseases.

4. Helps in controlling the diseases. To break the weakest link in chain of transmission of communicable diseases and reducing non communicable diseases.

5. Helps in planning of health programs on evidence basis and setting up of health priorities.

6. Helps to evaluate health programs andinterventions.

7. Helps to determine the chances or probability of occurrence of disease/ deaths and disability

8. Helps in better management of health services and hospital services.

9. Helps to set-up cut-off levels between normal and abnormal population andestablish trigger levels for action or intervention.

Sources of Sources of epidemiological epidemiological MeasurementsMeasurements

1. Cross sectional surveys2. Medical records3. Death certificate4. Census5. Organizational data

Domains of epidemiologyDomains of epidemiology Descriptive epidemiology

Descriptive epidemiology is the most Basic form of epidemiology. It is concerned with the description of the patterns of occurrence of health-related status or events in groups.

The determination of frequency and distribution of disease, incidence, prevalence, and mortality rates are included in descriptive epidemiology.

Analytical epidemiology

Analytical epidemiology is based on the observations made in the descriptive epidemiology. The design, execution andanalysis of subjects between groups helpsevaluate potential association between risk factors and health outcomes to answer the question “why?”.

Analytical epidemiology consists of two types of research processes

1. Observational process2. Experimental studies

Basic triads of descriptive and Basic triads of descriptive and analytical epidemiologyanalytical epidemiology

There are two different triads (3 essential components) considered in studying different sections

Descriptive epidemiology

Analytical epidemiology

Time (when) Host

Place (where) Agent

Person (who) Environment

Triad of descriptive Triad of descriptive epidemiologyepidemiology

Time

Changing or stable Seasonal variations Secular trends (long-term study of

incidence) Point source or propagated Cyclical variations (spikes of

incidences at regular intervals)

Place

Geographically restricted or wide spread

Relation to water and food supply Multiple cluster involvement or one Rural/Urban distribution

Triad of descriptive Triad of descriptive epidemiologyepidemiology

Person

Age Socio economic status Gender Ethnicity / Race Behavior

Triad of descriptive Triad of descriptive epidemiologyepidemiology

Triad of analytical Triad of analytical epidemiologyepidemiology

Agent Nutrients Poisons Allergens Radiation Physical trauma Microbes Psychological factors

Host factors

Genetic factors Immunologic state Age Personal behavior

Triad of analytical Triad of analytical epidemiologyepidemiology

Environment

Overcrowding Atmospheric changes Modes of transmission

VectorVehicleReservoir

Triad of analytical Triad of analytical epidemiologyepidemiology

Clinical epidemiology

When periodic observations are made over a long period of time in patients with a wide spectrum of clinical manifestations of the disease, a complete profile of the natural history of the disease may be obtained.

This forms the basis of clinical epidemiology.

Epidemiology of diseasesEpidemiology of diseases

Sri Lanka is said to be facing a double disease burden due to communicable and non communicable diseases (NCD) today.

What is triple burden???

The diseases burden in the country is given in terms of (apart from basic measures)1.Years of potential life lost2.Life expectancy free from disability3. Disability adjusted life years lost – DALYs4.Quality adjusted life years lost - QUALYs

loss per 1000 population.

Country has to fight to control communicable and non communicable diseases.

Epidemiology of communicable Epidemiology of communicable diseases (CCD)diseases (CCD)

Definition :- Communicable disease

A communicable or infectious disease is an illness caused by transmission of a specific infectious agent or its toxic products from an infected person or animal to a susceptible host, either directly or indirectly through an intermediate animal host, vector or inanimate environment (Last 1995)

Man to man

Animal to man

Disease TransmissionDisease Transmission

What is an Epidemic?What is an Epidemic?

It is the occurrence of cases of illness, specific health related behavior or other health related events clearly in excess of normal expectancy in a community or region.

An Endemic diseaseAn Endemic disease

A disease that usually present in a population or given area at a relatively high prevalence and incidence rates in compared to other areas.

E.g. Malaria is an endemic disease in Polonnaruwa

Major emerging and re-emerging Major emerging and re-emerging infectious diseasesinfectious diseases

1. HIV/AIDS2. Hepatitis B and Hepatitis C3. Tuberculosis4. Dengue5. Malaria6. Japanese encephalitis7. Plague8. Cholera

Major reasons for emergence of Major reasons for emergence of infectious diseasesinfectious diseases

High population growth, uncontrolled and unplanned urbanization,

Poor environmental sanitation, Migration of population, Natural disasters, Growing international trade, tourism and rapid travel, Alterations in microorganisms, Resistance to antimicrobials, Insecticide resistance, Weak public health system. Illiteracy and ignorance.

Chain of infection or chain Chain of infection or chain of transmissionof transmission

Infectious agent Transmission process Host

ENVIRONMENTS

Infectious agent

Pathogenicity Virulence Infectivity

This is the second important link in the chain of infection.

Transmission is defined as “Spread of infectious agent through the environment or toanother person, from the reservoir and source”.

Transmission processTransmission process

Methods of transmissionMethods of transmission

Direct and Indirect

Direct methods of Direct methods of transmissiontransmission

Touching Kissing Sexual intercourse Child birth Breast-feeding Air borne, short distance via droplets

(by coughing, Laughing, sneezing, spitting). Transfusion of blood Transplacental from mother to fetus

Indirect transmissionIndirect transmission

Vehicle borne transmission (by contaminated food and water)

Vector borne transmission Parenteral by unsafe injection Fomite transmission Unclean hands

Control of communicable Control of communicable diseases (CCD)-discuss diseases (CCD)-discuss

under 5 headingsunder 5 headings

1. Control of infectious agents in the environments

2. Control of infectious agent in host3. Control of outbreaks of CCD4. Other measures5. Specific measures for control of HIV

epidemic

(1)(1) Control of infectious Control of infectious agents in the environmentsagents in the environments

Controlling sources of infection1. Supply of safe drinking water by treatment and

chlorination of water, pasteurization of milk.2. Safe disposal of human excreta and animal excreta by

sewerage system and sanitary latrines, compost pits/manure pits.

3. Control vectors of diseases – by source reduction and anti-larval and anti-adult measures.

4. Animals – vaccinate dogs against rabies and eliminate street dogs.

5. Rodent control measures-trapping and killing6. Hospital waste management7. Disinfections

(2)(2) Control of infectious Control of infectious agent agent in in hosthost

1. Reservoir control2. Practice of chemoprophylaxis3. Surveillance4. Notification5. Quarantine

1. Complete quarantine2. Modified quarantine

6. Isolation7. Education and behavior

(3)(3) Control of outbreaks of Control of outbreaks of CCD-different steps will beCCD-different steps will be

discussed laterdiscussed later

Communicable diseases like Malaria, JE, DHF , Hepatitis E & A, Hepatitis B andDiarrhoeal diseases quite often occur inepidemic proportion. Many local and focal outbreaks are being reported quite frequently;Hence, control of outbreaks of these diseases is an essential requirement.

(4)(4) Other measuresOther measures

1. Legislation

Epidemic disease control act. And notification helps control of CCD.

2. Observe international health regulations

Notifiable diseasesNotifiable diseases

Group A

• Cholera• Plague• Yellow fever

Group B

• Rubella• Diphtheria• Enteric fever• Food poisoning• Leptospirosis• Measles• Tuberculosis

• Whooping cough• Acute anterior poliomyelitis• Simple continued fever of over seven

days• Dengue• Dysentery • Encephalitis

• Human rabies• Malaria• Tetanus• Typhus fever• Viral Hepatitis

Epidemiology of non-Epidemiology of non-communicable diseases (NCD)communicable diseases (NCD)Non communicable diseases cover wide

range of heterogeneous conditions affecting different organs and systems of different socioeconomic groups.

Over the last two decades morbidity and mortality due to cardiovascular diseases, mental disorders, cancer and trauma have been rising due to following causes.

CausesCauses

1. Rise in life expectancy and increasing number of senior citizens.

2. Changing life styles: Faulty diet, use of alcohol, sedentary life-physical inactivityand rising stress-leading to obesity and stress related problems.

3. Exposure to environmental risk factors-air pollution.

4. Use of tobacco

5. Increasing population and rise in automobiles and trauma incidence.

ImplicationsImplications

In view of the chronic morbidity and high cost involve in the management of non-communicable diseases attention need to be focused on prevention, early detection and appropriate management. Further, these diseases cause lot of disability and dependency and disease burden.

Multi - factorial originMulti - factorial origin

Causes of NCD are multi-factorial. Range of life styles: risk taking behavior, changing dietary pattern, physical inactivity, use of alcohol and tobacco and stress in life have been incriminated.

FutureFuture

For non-communicable diseases throughout the all levels of care so as to reduce morbidity and mortality.

1. Well-structured information education andcommunication for primary and secondary prevention of NCD.

2. Reorientation and skill up gradation of health care providers

3. Establishment of Referral linkages between primary secondary and tertiary institution.

4. Production and provision of drugs for NCD.

5. Development of institution for rehabilitation of disabled persons due to NCD, teaching persons to live with their disability.

6. Development of hospices for terminally ill people who cannot have home based care.

7. Creation of epidemiological database on NCD especially, CVD’s, strokes and diabetes.