• Bioterrorism Case Definitions The use of case definitions is very important in epidemiology in order to standardize criteria for identification of cases. A "case", in epidemiology, is a person in the population identified as having the particular disease or condition under investigation. A variety of criteria may be used to identify cases, e.g. individual physician's diagnoses, registries and notifications, and population screening, among others. The epidemiological definition of a case is not necessarily the same as the ordinary clinical definition. Centers for Disease Control and Prevention case definitions for infectious conditions under public health surveillance are available here.