In epidemiology, what is the effect of a highly sensitive case definition on surveillance?

• A. It increases the ability to identify true cases (higher sensitivity) at the cost of more false positives.
• B. It decreases the number of false positives.
• C. It has no impact on the number of cases identified.
• D. It always perfectly distinguishes disease.

Answer: (A)

A highly sensitive case definition increases the ability to identify true cases by casting a wide net. In surveillance, sensitivity is the probability that a person with the disease is classified as a case; making the definition more sensitive catches more of these true cases, but it also includes more people who do not have the disease, increasing false positives. This trade-off means more total cases are labeled as cases, though with reduced precision. The other statements imply fewer false positives, no change, or perfect discrimination, which does not align with how increasing sensitivity works.