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Session 1: Introduction toEpidemiology

Avhinesh

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WHAT IS EPIDEMIOLOGY?

Originated from Greek words

Epi: upon

Demos: people Logy: study of

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Epidemiology Definition

Epidemiology is the study of thedistributionand determinants ofhealth related events in specifiedpopulations and the application of thisstudy to control of health problems

( Last, 1995)

Beaglehole, Basic Epidemiology

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Epidemiology

A study or a systematic method of enquiry

Looks at distribution( what, where, when, who and

frequency ( how many) of health problems and disease or healthrelatedevents counting and calculation involved

looks at determinants = looks at risk factors that influence the

distribution of health related events

studies populations = interested in characteristics of groups of peoplerather than individual persons

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Epidemiology

Epidemiologists are concerned not only withDEATH, ILLNESS and DISABILITY, butalso with MORE POSITIVE HEALTH

STATES and with the means to IMPROVEHEALTH Epidemiology

Health

Disease

Population

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Epidemiology

Historically epidemiology was developedin order to investigate infectious disease.

Epidemic : is the occurrence in acommunity or region of cases of anillness, specific health related behaviour,or other

Endemic: refers to the ongoing, usual,or constant presence of a disease in acommunity.

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Epidemiology

Pandemic is an epidemic affecting orattacking the population of an extensiveregion, country, or continent.

Epidemics are often described by howthey spread through the population.

Two primary types of infectious-diseaseepidemics are common source andpropagated epidemics.

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Epidemiology

Common-Source epidemic: arise froma specific source.(infected water, well)

Propagated epidemics: arise frominfections transmitted from person toperson. Transmissions can be direct orindirect routes.(TB, Rubella)

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Phases of Epidemiology

In some text three phases are discussed whilein others there are four phases.

In both cases basic principles are same

These include:

1. DescriptiveEpidemiology

2. AnalyticalEpidemiology

3. Interventional / Experimental EpidemiologyEvaluation Epidemiology

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Descriptive Epidemiology

Concerned with the distribution andfrequencyof disease or health relatedevents

Questions asked:

what? problem and its frequency

who? .. Person where? .. Place

when? time

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Analytical Epidemiology

Attempts to analyze the causesordeterminantsof disease or healthrelated events

Questions asked:

how is the disease caused?

why is it happening/ continuing? Through:

hypothesis testing

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Interventional / Experimental AndEvaluation Epidemiology

Concerned with evaluating andmeasuring the effectiveness of new andor alternative interventions

Clinical and community trials are used Questions asked: what if? how effective is the intervention? have there been any improvements in

health status?

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Epidemiology

Descriptive and evaluation epidemiologyis extremely useful and frequently used,especially in the Pacific

Analytical and experimentalepidemiology are not used so often ( inPacific) because they rely on

complicated research methods. i.e. case control studies, cohort studies, clinicaland community trials

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Population at Risk

Is the population made up of people who are healthy andunhealthy but who have the potential to develop the healthevent of interest

Reference population from where the cases are taken Include those who are exposed to a disease agent,

unimmunized, risk categories ( occupational injuries),population of country, town, city.

Have the potential to get the disease and thus may contributeto the total number of cases

Used for developing population needed for health planning,management of health programs and evaluation of healthpromotion and disease control activities

E.g. Coverage for immunization

Coverage is a measure of the percentage of people orhouseholds in need of a service of facility who actually receiveit

Higher coverage is better

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Uses of Epidemiology

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Natural History of Diseases

Natural history of disease is the courseof disease overtime unaffected bytreatment

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STAGES

1. Stage of susceptibility

Disease has not developed but thegroundwork has been laid by thepresence of factors that favour itsoccurrence (risk factors).

For example, smoking, alcoholism andstress are the risk factors forhypertension.

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2. Stage of pre symptomatic disease

Pathological changes have started butasymptomatic (incubation period, latencyperiod).

For example, arthrosclerosis ishappening but still undetected at clinicalstage.

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3. Stage of clinical disease

By this stage sufficient changes haveoccurred so that person manifests signsand symptoms of disease.

For example, patient may show signsand symptoms of hypertension like highblood pressure readings and dizziness.

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4. Stage of disability/ recovery.

Disease has run its course and resolvedspontaneously with therapy. However forsome conditions there maybe residual

defect of long or short term duration.

For example, if proper treatment was notinstituted to the hypertensive patient then

they may have stroke.

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Levels of Prevention

1. Primordial Prevention

Aim at providing the emergence ofconditions that leads to increased risk ofdisease. It requires policies and fiscalaction to stop promotion of risk factors.

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2. Primary Prevention

It prevents the occurrence of disease byminimising risk factors. For exampleimmunization, seat belts, OHS laws, anti

smoking campaigns, general healthpromotion on hygiene, good nutrition andchlorination of water.

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3. Secondary Prevention

It involves early detection and prompttreatment of disease. There is possibilityto cure disease or slow the rate or

progression or prevent complications.Requires screening by health workers.For example do pap smears, and routine

blood checks.

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4. Tertiary Prevention

It consists of activities that preventfurther deterioration or minimisecomplications on a person who has a

disease. Disease has already occurredbut there are rehabilitation attempts torestore an affected individual to maximal

function

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Historical OverviewThe First Epidemiologists

THE FIRST EPIDEMIOLOGISTS

Hippocrates ( 460 -377 BC) recognizedassociation of disease with place (

geography), water conditions, climate eatinghabits and housing. Used terms epidemicand endemic" believed disease was result ofimbalance in the bodys humors.

Galen ( 129- 199AD) lifestyle factors andpersonality can influence health and disease.Miasma theory bad air caused disease

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Historical OverviewThe First Epidemiologists

T. Sydenham ( 1624 -1689)Observations should take precedenceover theory in the study of the natural

history of disease

N. Webster(1758-1843)- Epidemicswere related to certain environmental

factors.

Historical Overview

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Historical OverviewThe Concept of Contagion and Germ Theory ofDisease

E. Jenner prevented smallpox

infection by inoculating healthy peoplewith cowpox

L. Pasteur showed immunization

prevented rabies. Dispelled miasmatheory.

Hi i l O i

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Historical OverviewBirth of Vital Statistics

J. Graunt first to quantify patterns ofbirth, death and disease occurrence,noting malefemale disparities, high

infant mortality, urban rural differencesand seasonal variations

W. Farr looked at effects of marital

status, occupation and attitude.Developed concept of mortalitysurveillance

Hi i l O i

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Historical OverviewEarly Classic Epidemiologic Studies

J. Lind (1735) Experimental epidemiologicstudy of the etiology and treatment of scurvy.Concluded eating citrus treated scurvy andwould prevent its occurrence. Lead to British

navy requiring limes or lime juice in seamensdiet. How British seamen became known as limeys

P.L.Panum. studied measles on FaroesIslands. Concluded measles transmitted by

direct contact between infected andsusceptible individuals. Suggested one attackof measles conferred lifelong immunity

Hi i l O i

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Historical OverviewEarly Classic Epidemiologic Studies

J. Snow (1813-1858) Father of FieldEpidemiology 20 years before

discovery of the microscope, conductedstudies of cholera outbreaks. Used spotmaps to show case distribution. Believed

water was source of infection. Removedhandle to Broad Street pump to controlepidemic.

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Achievements in Epidemiology

Elimination of smallpox Methyl mercury poisoning Rheumatic fever and rheumatic heart

disease Iodine deficiency disease High blood pressure Smoking and lung cancer HIV/ AIDS.

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Epidemiology a way of asking questions

and obtaining answers leading to further

questions to be answered What is the event/ problem?

What is the magnitude?

Where did it happen? When did it happen?

Who are affected?

Why/ how did it happen?

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who (Host)

where (Envir) what( Agent)

Epidemiological Triangle