Investigation of an Epidemic – Objective and Steps.
Introduction
Investigation of an Epidemic is an epidemic always signals some significant shift in the existing balance between the agent, host and environment. It calls for a promote and through investigations of the cases to uncover the factors responsible and to guide in advocating control measure to prevent further spread. Epidemiology has an important role to play in the investigation of an epidemic.
Objective
The objective of an epidemic investigation are-
i) To define the magnitude of epidemic outbreak or involvement in terms of time, place, and person.
ii) To determine the particular condition and factors responsible for occurrence of the epidemic.
iii) To identify the cause, source of infection and mood of transmission.
iv) To make a recommendation to prevent recurrence.
Steps for epidemic investigations
1. Verification of diagnosis:
Verification of diagnosis is the first step of in an epidemic investigation, as it may happen sometime that the report may be spurious, and arise from misinterpretation of sign and symptoms by the Lay public. It is therefore necessary to have the verification of diagnosis as on the spot, as quickly as possible.
2. Confirmation of the existence of an epidemic:
The next step is to confirm if epidemic exists-
i) Comparing the disease frequency during the same period of previous years.
ii) Some common source epidemics of cholera, food poisoning, hepatitis etc., no comparison is required.
3. Defining the population at risk:
i) Obtaining a map of the area:- Before beginning the investigations, it is necessary to have a detail and current map in the area. If this is not available, it may be necessary to prepare such a map. It should contain information of natural landmarks, roads and locations of all dwelling unit along each road or in isolated areas.
ii) Counting the papulation:- Population is counted by house to house visit. The population census may help
4. Rapid search for all cases and their characteristic:
i) Medical survey:- Screening of each member of the population for the presence of disease in questions.
ii) Epidemiological case:- It should be carefully designed to collect relevant information. This include name, age, sex, occupation, travel, social class, sign and symptoms of illness, personal contacts at home, work, school and other places, history of previous exposure, etc.
iii) Searching for more cases:- The patient may be asked if he new other cases in the home, family, neighborhood, school, work place, etc.
5. Data analysis:
The data collected should be analyzed on ongoing basis, using time, place and person.
i) Time:- Time and dates of onset and epidemiological curved should be prepared.
It may suggest-
a) Timeless relationship with exposure to a suspected source.
b) Whether it is a common source or propagated epidemic.
c) Whether it is a seasonal or cyclic pattern.
ii) Place:- Spot map (graphical distribution) should be prepared. Clustering of cases may indicate a common source of infection.
iii) Person:- Analyze the date by age, sex, occupation and other possible risk factor.
6. Formulation of hypothesis:
Hypothesis is formulated on the basis of time, place and person or the Agent-Host-Environment.
7. Testing of hypothesis:
All reasonable hypothesis need to be be considered and weighed by comparing the attack rates in various groups of those exposed and those not exposed to each suspected factors.
8. Evolution of ecological factor:
The disease should be related to environmental factors to know the source of infection, reservoir and moods of transmission.
9. Further investigation of Population at risk:
i) The study Population at risk may be needed to obtain additional information.
ii) This may involve medical exams, screening tests, exam of suspected foods, faces or blood sample, biochemical studies, assessment of immunity, status etc. The approach may be retrospective or prospective.
10. Writing a report:
The report should be complete and convincing. Information to be included in the report consist of the following-
i) Background information:-
- Geographical location
- Climate condition
- Demographic status
- Socio and economic situation
- Organization of health service
- Normal disease prevalence
ii) Historical data:-
Previous occurrence of epidemic of some disease locally or elsewhere.
iii) Methodological of investigation:-
- Case definition, Questionnaire used in the epidemiological investigation.
- Survey team- household survey, retrospective survey, prospective surveillance, collection of laboratory, specimen, laboratory techniques.
iv) Analysis data:-
- Clinical data
- Epidemiological data
- Modes of transmission
- Laboratory data
- Interpretation of data.
v) Control measure:-
- Definition of strategies and methodology of implementation.
- Evolutions.
- Preventive measure.
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| Steps for epidemic investigations |
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