In this course, we have often assumed that investigators have knowledge of a potentially harmful exposure coincidentally with or prior to observing the disease or illness. In other situations, the first indication of harmful exposure is a report of a potential outbreak of disease or illness. Increased numbers of cases of disease or illness may necessitate an outbreak investigation. Questions to be answered in an outbreak investigation include the following:

1. Are there an unusual number of adverse health outcomes in this community?
2. If so, how many? Is the number increasing, decreasing, or stable?
3. What type of exposure may have caused the increase?
4. What is the anticipated future course and spread of this outbreak?

Basic case-control studies are very useful when investigating an outbreak of disease. Last week we studied the basic case-control study. This week we will see some more advanced case-control designs, but these are rarely used in outbreak investigations because they take longer to implement and are more complex.

Let's get started!