What does a case definition typically specify in an outbreak investigation?

• A. Only the laboratory result
• B. Clinical criteria and, if applicable, laboratory criteria and time/place
• C. Only the geographic location
• D. Only the age group affected

Answer: (B)

In an outbreak investigation, a case definition is a standardized description used to identify who counts as a case. It typically combines the clinical criteria—the signs and symptoms that define the illness—and, if available, laboratory criteria to confirm infection. It also specifies the time frame and place to focus the search and to distinguish outbreak-related cases from background cases. This combination allows consistent identification of cases and helps map the outbreak’s scope.

Including all three elements—clinical features, lab confirmation when possible, and time/place—is essential because relying on only one element can either miss true cases (if you skip clinical or lab data) or include non-outbreak illnesses (if you ignore the temporal and geographic boundaries). The time and place help constrain the definition to the outbreak period and area, making the investigation more precise and actionable.