An epidemic occurs when there is an unusual increase in the occurrence of a disease within a community or region beyond what is normally expected. To determine if an epidemic has occurred, one must consider the magnitude of cases, factors responsible, and cause/mode of transmission. Investigating an epidemic involves 10 steps: 1) verifying diagnoses, 2) confirming the epidemic's existence, 3) defining the at-risk population, 4) rapidly searching for all case characteristics, 5) analyzing data, 6) formulating hypotheses, 7) testing hypotheses, 8) evaluating ecological factors, 9) further investigating the at-risk population, and 10) writing a report of the background, methodology, data analysis, and control recommendations.

1. Dr Pallavi Potdar
Associate Prof.,
Community Medicine
D.Y. Patil Medical College Kolhapur

2.  Epidemic ?
 Def- the unusual occurrence in a community or
region of a disease, specific health- related behaviour
or other health-related events clearly in excess of
expected occurrence.
 John Snow

3.  When to call epidemic has occurred ?

4. 1) Magnitude of epidemic outbreak
2) Factors responsible
3) Cause, source of infection, modes of transmission
4) Recommendations to prevent recurrence

5. 1) Verification of diagnosis
2) Confirmation of existence of epidemic
3) Defining population at risk
4) Rapid search for all cases ,characteristics
5) Data analysis
6) Formulation of hypothesis
7) Testing of hypothesis
8) Evaluation of ecological factors
9) Further inv of population at risk
10) Writing the report

6. 1) Verification of diagnosis-
sample of cases
clinical examination
If possible laboratory investigations

7. 2) Confirmation of existence of epidemic-
Compare the disease frequencies during the same
period of previous 3 years.

8. 3) Defining the population at risk-
-spot map
-counting the population
4) Rapid search for all cases and their characteristics-
- medical survey
- epidemiological case sheet
- searching for more cases

9. 5) Data analysis- time , place , person
Time- epidemic curve
Place- spot map
Person-age, sex , occupation

10. 6) Formulation of hypotheses-
Possible source
Causative agent
Possible modes of spread
Environmental factors

11. 7) Testing of hypotheses-
8) Evaluation of ecological factors-
breakdown in water supply system
sanitary status of eating establishment
temperature, humidity

12. 9) Further investigation of population at risk-
Medical examination
Screening tests
Food, faeces, blood samples

13. 10) writing the report-
a) Background
b) Historical data
c)Methodology of investigation
d)Analysis of data
e)Control measures

14. a) Background- geographic location
climatic conditions
socio-economic situation
normal disease prevalence
surveillance

15. b) Historical data- previous occurrence of epidemic of
same disease.
c) Methodology of investigations-
case definition
questionnaires used
household survey
retrospective survey
prospective survey
laboratory techniques

16. d) Analysis of data-
clinical data
epidemiological data
modes of transmission
lab data
interpretation of data
e) Control measures-