An Epidemiological Investigation
1. Is it an outbreak? Determine if the disease is common to the area or if it has been reported in the area previously. An outbreak has occured when the number of infections reported is higher than the expected number of infections.
2. Identify the specific nature of the disease. To verify the diagnosis, review clinical findings (symptoms and featurse of the illness) and laboratory results of the peopel who are affected. Visit several of the people who became ill and talk to some of the infected to gain a better understanding of the disease and those affected by it. In addition, you may be able to gather critical information by asking such questions as, what were their exposures before becoming ill? What do they think caused their illness? Do they know anyone else with the disease? Do they have anything in common with others who have the disease? Conversations with patients are very helpful in generating hypotheses about the cause, source, and spread of disease.
3. Define the disease. Create a definition based on the symptoms. This should include a defined method for determining if a person is infected with this disease.
4. Determine the number of people infected. Determine the risk factors: How many people were exposed, in what area, over what period of time? Information about risk factors will tailor your investigation to the specific disease in question.
5. Create a hypothesis based on information on everyone infected along with specimens collected through field work.
6. Test the hypothesis. Analytic epidemiology tests your hypotheses by using a comparison group to quantify relationships between various exposures and the disease.
There are two types of analytic studies: cohort studies and case-control studies.
Cohort studies compare groups of people who have been exposed to suspected risk factors with groups who have not been exposed.
Case-control studies compare people with a disease (case-patients) with a group of people without the disease (controls). The nature of the outbreak determines which of these studies you will use.
7. Control measures should be aimed at specific links in the chain of infection, the agent, the source, or the reservoir.
