Epidemiology Intro

8/13/2019 Epidemiology Intro

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EPIDEMIOLOGY- INTRODUCTION


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What is Epidemiology?

Epi = Among

Demos = People

Logos = Study


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Study of disease occurrence in human population

Study of the distribution and determinants ofhealth related states or events in a specified

population.

What is Epidemiology?


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Exposure:Any characteristic associated with either an increased or decreased

occurrence of disease or event of interest.

-Risk factor/ Protective factor

Outcome

A broad term for any defined disease, state of health, health- related

event or death

Multiple outcomes?

NB: The exposure of interest in one study may be the outcome in

another.

Epidemiology


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Research Questions?

Does smoking increases the risk of lung cancer?

Does less salt intake protect against hypertension?


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Epidemiology

Primary units are groups of people

3 questions

Who? - Person

When? - TimeWhere? - Place


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Historical Notes

o John Snow (Father of Epidemiology)

o Cholera epidemic in London1853-54

o Formulated & tested the hypothesisabout the origin.

o Compared cholera death rates indifferent areas in London.

o On the basis of available data source,he postulated that cholera wastransmitted through contaminated water


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Development of modern epidemiology

The broadening of the term Epidemic

Any disease or any disease determinant

Endemic: The habitual presence of a disease with in a givengeographical area.

Epidemic: An increase in incidence above the expected in a

defined geographic area within a defined time period.

Pandemic: Worldwide Epidemic


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Need for new methodology

- Long latency time (time between exposureand clinical appearance of disease)

- Multi-factorial etiology (Genetic,

environmental, lifestyle, psychosocial, etc)


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Pioneers of Modern Epidemiology

Case-control design: Developed to address long latency periods

Smoking and lung cancer Doll and Hill -1945

Cohort design:

Collecting exposure information prior to the event

Framingham Heart study

Great Britain Male Physician study (Doll & Hill since 1951)

Seven countries study (first ecological and later cohort study)


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Richard Doll and A. Bradford Hill. Smoking

and carcinoma of the lung, British

Medical Journal 1950: Sept 30.

(Republished Bull WHO 1999; 77:84-93).


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Global disease burden: Changing disease pattern

Urbanization

Changing lifestyles

Aging

Socio-economic networking

New diseases


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Specific Objectives of Epidemiology

To determine the magnitude of disease

To identify the etiology or the cause of a disease and its riskfactors

To study the natural history and prognosis of the disease

To evaluate both existing and new preventive and therapeuticmeasures and new modes of health care delivery

To provide foundation for developing public policy and makingregularity decisions relating to environmental problems


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Epidemiological Triad of a disease

Agent Host

Environment

A disease is the product of an interaction of the human host, an

infectious or other type of agent and the environment that promotes

the exposure.

Vector


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Examples of Agents of Disease

Nutritive excesses or deficiencies (Cholesterol, vitamins,proteins)

Chemical agents (carbon monoxide, drugs, medications)

Physical agents (Ionizing radiation)

Infectious agents (hookworm, malaria, tuberculosis, syphilis,polio, rabies, mumps, etc.)


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Examples of Host Factors

Age

Personal behavior (diet, recreation, use of

resources, etc)

Immunologic state

Genetic endowment


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Examples of Environmental Factors

Crowding

Atmosphere

Modes of communication phenomena in the

environment that bring host and agent together, such

as:

Vector

Reservoir, etc.


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Information in Epidemiological studies

Collect information on 3 types of variables

Primary exposure(s) of interest

Other exposure(s) that influences outcome :

Potential confounder

The outcome(s)


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Types of exposure

Genetic traits (eg: Blood group) Demographic variables (sex, age, ethinicity, SES, etc)

Reproductive variables

Diet & body fluid

Physical activity

Smoking & alcohol habits

Past medication (eg: oral contraceptive use)

Environmental exposure

Occupational exposure, etc.


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By personal interview/ self administeredquestionnaire/ diaries of behavior/ reference to

records/ biological measurements.

Information on

- Nature of the exposure

- Dose/ amount- Time (beginning/ end point)

Measurement of exposure


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Questionnaires

- Self administered

- Interviewer administered

Diaries

Detailed records of exposure kept by the subject

Records

Medical/ birth/ death certification records, etc

Sources of exposure

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Biological measurements

Laboratory assays to ascertain exposure to

infectious agent HPV (Cervical cancer) &

Helicobacter Pylori (Stomach cancer)

Measurements in the environment

Include agents in air (air pollutants, dust), water

(Fluoride), soil ( elements), food (nutrient

composition) etc.

Sources of exposure

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Questionnaire/ telephone calls

Periodic personal interviews with clinical check

ups- Biological measurements

Hospital records/ death certificate

Measurement of outcome

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Data

Different types of Data?

Sources of data

Census

Registration of vital events

(Death certification:International Classification of

Diseases)

Sample Registration System?

Hospital records

Cancer registries (Hospital/Population based)

Record linkage :

(Information on individuals from birth to death isavailable in records usin ersonal identifier


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Documents

Epidemiology Intro