What is a case definition?

• A. A System for Identifying Patients Who Have an Infection at Discharge
• B. A Statistical Method for Estimating Disease Incidence
• C. A Method Used to Determine Which Cases Should Be Included in a Registry
• D. A Protocol for Reporting to Public Health Authorities

Answer: (C)

A case definition is the set of explicit criteria used to decide whether a person with certain signs, symptoms, or test results is considered a case for surveillance and data collection. This standard ensures that everyone classifies cases the same way, which is essential for accurate counting and comparison over time and across locations. A typical case definition combines clinical features, laboratory confirmation, and sometimes epidemiologic information such as exposure or time frame. By applying this definition, you determine which individuals are included in a registry, keeping the data consistent and reliable. The other options describe different ideas—identifying patients at discharge, using statistical methods to estimate incidence, or following a protocol for reporting to public health agencies—which are not about deciding who meets the standardized criteria to be counted as a case.