Investigation of an epidemic

Investigation of an epidemic

1. Investigation of an epidemic Dr. Arkadeb Kar

2. Epidemic The unusual occurrence in a community or region of disease, specific health related behavior (e.g. Smoking) or other health related events (e.g. Traffic accidents) clearly in excess of expected occurrence.

3. Objectives 1. To define the magnitude of the epidemic outbreak or involvement in terms of time, place & person. 2. To determine the particular condition and factors responsible for occurrence of the epidemic. 3. To identify the cause, source(s) of infection and mode of transmission. 4. To implement immediate control measure. 5. To make recommendation to prevent recurrence.

4. Steps for Epidemic investigation Verification of diagnosis. Confirmation of the existence of an epidemic. Define and identify cases Defining the population at risk. Rapid search for all cases and their characteristics.

5. Steps for Epidemic investigation Data analysis. Formulation of hypothesis. Testing of hypothesis. Evaluation of ecological factor. Further investigation of population at risk. Writing a report Implement control and preventive measures

6. Verification of diagnosis First step in an epidemic investigation. A clinical exam. of a sample of cases. Lab. Investigations done if necessary.

7. Confirmation of the existence of an epidemic Comparing the disease frequencies during the same period of previous years. Some common source epidemics of cholera, food poisoning, hepatitis etc., no comparison is required .

8. Define and identify cases Case definition should be broad enough to include most, if not all, of the actual cases. Usually includes four components: clinical information about the disease, characteristics about the people who are affected, information about the location or place, and a specification of time during which the outbreak occurred

9. Possible (suspected) New or Worsening of cough, Fever >38, nasal discharge, sore throat Probable Symptoms +Radiology evidence Definite (confirmed) Laboratory confirmed

10. Defining the population at risk Obtaining a map of the area – Map is prepared, if not available. It should contain information of natural landmarks, roads and location of all dwelling units along each road or in isolated areas. Counting the population – population is counted by house to house visit. The population census may help .

11. Case finding Medical surveys - Screening of each member of the population for the presence of disease in question Epidemiological case sheet – should be carefully designed to collect relevant information Searching for more cases – The pt. may be asked if he knew other cases in the home, family, neighbourhood , school, work place etc.

12. Data analysis Data should be analyzed on ongoing basis, using time, place and person. Time – Time and dates of onset and epidemiological curve should be prepared. It may suggest 1. a time relationship with exposure to a suspected source 2. whether it is a common source or propagated epidemic. 3. whether it is a seasonal or cyclic pattern.

13. Place– Geographic extent of problem Clusters or patterns providing important etiologic clues Spot map should be prepared. Clustering of cases may indicate a common source of infection.

14. Person – Determine what population at risk Define population by host characteristics or exposure Use attack rate to identify high-risk groups

15. Formulation of hypothesis Hypotheses should address Type of exposure The agent and its reservoir Mode of transmission Risk factors that caused disease

16. Testing of hypothesis All reasonable hypotheses need to be considered and weighed by comparing the attack rates in various groups for those exposed and those not exposed to each suspected factor

17. Evaluation of ecological factors The disease should be related to environmental factors to know the source of infection, reservoirs and modes of transmission. Investigate ecological factors – Sanitary status, water supply, food hygiene, pollution, migration etc.

18. Further investigations of population at risk The study population at risk or a sample of it may be needed to obtain additional information. This may involve medical exam., screening tests, exam. of suspected food, faeces or blood sample, biochemical studies, assessment of immunity status etc.

19. Writing a report to communicate Local health authorities and persons responsible for implementation of control and prevention measures Control measures It should start as soon as possible May be aimed at agent, source, or reservoir Short or long term (reducing susceptibility)