Epidemic investigation is a set of procedures used to identify the cause, i.e. the infectious agent, responsible for the disease. It is also used to identify the people affected, the circumstances and mode of spread of the disease, and other relevant factors involved in propagating the epidemic. This is especially important if the epidemic has unusual features, if it presents a significant threat to public health, and it is not self-limiting (i.e. it does not end spontaneously without professional intervention).
Epidemic investigation is a challenging task for health professionals. The main purpose of epidemic investigation is to control the spread of the disease before it causes more deaths and illness. The first action you should take is to confirm the existence of an epidemic. To do this, you need to know the average number of cases of that disease during this specific month in your community in previous years, so you can compare that number with the current number of cases. Is there an excess number of cases or deaths from this disease compared to the usual occurrence? If there really are excess cases, you should report your findings immediately.
The next steps (box below) will be taken by the appointed epidemic management team, which is composed of many different health professionals such as doctors, nurses, environmental experts and others. These steps include confirming the cause (the infectious agent involved), the number of people affected (the cases) and the modes of transmission of the infection from cases to new susceptible hosts.
Steps in an epidemic investigation
- Establish the existence of an outbreak
- Verify the diagnosis or causes
- Define and identify cases:
- Use a standard case definition
- Identify and count cases
- Perform descriptive epidemiology, i.e. collect data on the age, sex, etc. of the cases and analyse the data to see if useful patterns emerge
- Develop hypotheses to explain the occurrence of the epidemic:
- Evaluate the hypotheses
- Reconsider/refine the hypotheses
- Carry out additional studies to confirm or reject the explanations for the epidemic:
- Additional epidemiological studies
- Other types of studies, e.g. laboratory tests, environmental investigations
- Implement control and prevention measures
- Communicate findings to higher levels in the health system, community leaders and other local stakeholders.