In surveillance, case definition helps determine which cases should be included in a registry.

• A. To Measure Disease Severity
• B. To Determine Criteria for Including Cases in a Registry
• C. To Classify Pathogens by Species
• D. To Estimate Hospital Stay Duration

Answer: (B)

The main idea is standardizing what counts as a case for surveillance. A case definition provides the criteria used to decide which patients should be included in a registry, so every reporter applies the same rules. This standardization ensures data are consistent and comparable across reporters, jurisdictions, and time, which is crucial for accurate incidence estimates and trend analysis. Case definitions often combine clinical features with laboratory confirmation and may specify a time frame or setting, helping to include true cases while excluding non-cases.

This focus on inclusion criteria is what makes it the best choice. It isn’t about measuring how severe a disease is, classifying pathogens by species, or estimating how long a patient stays in the hospital. Those are separate questions or outcomes.