Give an example of sentinel surveillance and its purpose.

• A. Tracking every single case in the population to achieve exact incidence.
• B. Monitoring influenza-like illness in selected sentinel clinics to estimate national trends, providing early signals but not exhaustive population coverage.
• C. Using real-time hospital admissions to provide nationwide coverage.
• D. A surveillance system that relies on social media posts.

Answer: (B)

Sentinel surveillance uses a small, deliberate network of reporting sites to monitor disease indicators and detect trends or early signals without counting every case. An example is monitoring influenza-like illness in selected sentinel clinics to estimate national trends and provide early signals. This approach gives timely information and trend estimates while being more cost-effective and faster than full population coverage.

Why this fits: focusing on a subset of sites allows rapid data collection and early warning of changes in disease activity, which is the main purpose of sentinel systems. It does not aim to capture every case, which would require exhaustive population coverage.

Why the other options don’t fit: tracking every single case would be full population surveillance, not sentinel. Relying on real-time hospital admissions for nationwide coverage aims at complete coverage rather than a sentinel network. Using social media posts represents informal digital surveillance, not sentinel clinic-based monitoring.