• 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.

• Case definitions for Category A agents
The U.S. public health system and primary healthcare providers must be prepared to address various biological agents, including pathogens that are rarely seen in the United States. High-priority agents include organisms that pose a risk to national security because they can be easily disseminated or transmitted from person to person; result in high mortality rates and have the potential for major public health impact; might cause public panic and social disruption; and require special action for public health preparedness.