Which statement defines a case definition?

• A. Criteria that must be met for the patient to qualify as having the disease (based on clinical symptoms or test results)
• B. A general description of the disease
• C. A plan for patient follow-up
• D. The rate of new cases over time

Answer: (A)

A case definition is the standardized set of criteria used to decide whether a person is considered a case for surveillance or outbreak study. It specifies the clinical features and, when available, laboratory evidence that must be present, so different clinicians and sites count cases consistently over time and across places. The statement that describes criteria that must be met for the patient to qualify as having the disease (based on clinical symptoms or test results) captures this precisely. The other ideas aren’t about identifying who counts as a case: a general description of the disease is just an overview, a plan for patient follow-up is about management, and the rate of new cases over time is an incidence measure, not a definition used to classify individuals.