2. Introduction.
First phase of an epidemiological investigation.
Concerned with observing the distribution of disease
or health related characteristics in human
populations.
Basically ask three questions- when is disease
occurring?-time distribution.
Where is it occurring?-place distribution.
Who is getting the disease?-person distribution.
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3. Procedures.
1. Defining the population– because investigation is
on population but not an individuals.
Define population in terms of total number, age,
gender, occupation, cultural characteristics etc.
Defined population can be whole population or
representative, or a selected group in a geographical
area.
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4. Contd…
Defined population can be large enough, stable and
community participation, similar, health should be
available
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5. Procedures contd…
2. Defining the disease under study- definition by
which the disease or condition can be identified and
measured in the defined population with a degree of
accuracy.
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6. Procedures contd…
3. Describing the disease– in terms of time, place and
person.
This involves systematic collection and analysis of
data.
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7. Describing the disease—time
distribution.
Time of disease occurrence (week, month, year, day of
the week, hour of onset)
Helps to know source or etiology of disease.
So potential preventions can be taken.
There are three kinds of time trends or fluctuations in
disease occurrence.
Short time fluctuations
Periodic fluctuations.
Long-term or secular trends.
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8. Describing the disease—time
distribution contd…
Short time fluctuations– ex- an epidemic.
Definition- the occurrence in a community or region
of cases of an illness or other health related events
clearly in excess of normal expectancy.
Two types- common source epidemics and
propagated epidemics.
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9. Describing the disease—time
distribution contd…
Common source epidemics– a common source is
responsible for spreading the disease.
It may be single source or continuous or repeated
exposure.
Single exposure(point source)- food poisoning
Continuous or repeated exposure- water born
disease who use the same water.
propagated epidemics– origin is infectious and
person to person transmission.
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10. Describing the disease—time
distribution contd…
Periodic fluctuations- occurrence of disease for a
particular period of time.
Seasonal trend– ex- measles common in early spring,
GI infections common in summer.
Long term fluctuations (secular trends) these are
continuous long term changes in the frequency of
diseases occurring over many years or decades.
It is influenced by the degree of immunity in the
population, improved SE condition, awareness
The trends may be upward or downwards.
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11. Describing the disease—time
distribution contd…
Upward trend may be due to increased disease
awareness, improved diagnostic and treatment facility,
improved recording and reporting facility.
Downward trend- caused by favorable change in the
epidemiological behavior of a disease. Presently DM,
Heart diseases are showing up ward trend.
We can show these trends by graphs.
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12. Distribution by Place.
Distribution of disease may described as global, regional,
national or local.
Examine morbidity and mortality in relation to SE factors,
dietary differences in culture and behavior.
Global distribution—pattern of disease not same
everywhere.
Ex- malaria and leprosy tropical diseases.(hot & humid
climate)
National distribution– variations within the country.
In India many religions, belief, cultures these make
differences. Some parts are affected more and some are less
affected.
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13. Distribution by Place contd…
Regional distribution– it is a comparative study of
distribution of diseases within climatically homogenous
regions of the world.
Ex- oro pharyngeal cancer in India, cervical cancer in Shri
Lanka, breast cancer in Indonesia, and stomach cancer in
Mongolia.
Rural and urban variations are also present.
Chronic bronchitis, accidents, lung cancer, CVDs, mental
illnesses and drug dependents are common in urban areas.
Skin and soil transmitted worms are common in rural
areas.
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14. Distribution by Place contd…
Local distribution– inner and outer city variations.
These are studied by spot maps.
If there is clustering of cases in any area we can take
actions and preventive measures.
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15. Distribution by Person
Influenced by person’s personal characteristics.
Age– is strongly related to disease.
Certain diseases are common in particular age group.
Ex- measles is common in children, cancer in middle age
and atherosclerosis in old age.
Sex- thyrotoxicosis, cholecyctitis, diabetes, obesity,
arthritis, psychoneurosis are more frequent in women.
In men- peptic ulcer, cancer lung, CVDs, accidents are
common.
Women in her reproductive period is at risk of morbidity
associated with pregnancy and childbirth.
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16. Distribution by Person contd…
Occupation– may alter the habit pattern of
employees.
Ex- sleep, alcohol, smoking, drug addiction etc.
Disease is influenced by the main occupation of the
person.
Ex- agriculture – allergic reaction, worm infestation.
Industrial occupation—hazards of physical, chemical
exposures.
Ex- coal mines- silicosis, sedentary occupation- heart
diseases.
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17. Distribution by Person contd…
Marriage– promotes health and security of
individuals.
It influences their health habits, and life style.
Disruption in married life has adverse effect on health.
Residence– determines the nature of environment.
The infection, infestations, deficiency and zoonotic
diseases are common among rural folk.
In city people- chronic bronchitis, cancer, CHDs are
frequent.
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18. Distribution by Person contd…
Socio-cultural milieu- determines their habits,
customs, practices, beliefs which influence their
health.
Economic background– poor people suffers from
poverty associated diseases. Rich people suffers from
diseases of over nutrition, sedentary occupation and
stressful environment.
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19. 4. Measurement of Disease.
Diseases can be measured by tools of epidemiology such
as rate, ratio and proportions.
Rate- expressed in terms of mortality, morbidity,
disability.
Incidence and prevalence are the two components.
Results of the study are applied on whole population.
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20. 5. Comparing with known Indices.
Includes asking questions and making comparisons.
Compare with global, national, state and local data.
By comparison we come to know the disease etiology.
Can group the people with risks.
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21. 6. Formulation of Hypothesis
Hypothesis relating to disease etiology.
Ex- smoking of 30-40 cigarettes per day causes lung
cancer in 10% of smokers after 20 years of exposure.
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