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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
S f
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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
f
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Questionnaire/ telephone calls
Periodic personal interviews with clinical check
ups- Biological measurements
Hospital records/ death certificate
Measurement of outcome
D
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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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