Absent an outbreak, case definitions are used in the surveillance of public health in order to categorize those conditions present in a population (e.g., incidence and prevalence).
[3][4] Time criteria may include all cases of a disease identified from, for example, January 1, 2008 to March 1, 2008.
Place criteria will usually specify a geographical entity such as a town, state, or country, but may be as small as an institution, a school class, or a restaurant meal session.
Shared definition of the phenomenon impacts the study methods and ensures terminology is used in a consistent manner.
[5] The term diagnostic criteria designates a case definition with a specific combination of signs, symptoms, and test results that the clinician uses to attempt to determine the correct diagnosis.