Test-Negative Case-Control Study

The test-negative design reduces bias from healthcare-seeking differences because cases and controls sought care for similar symptoms. Controls are infants meeting the same acute respiratory illness criteria who test negative for RSV. Cases are infants with acute respiratory illness who test positive for RSV by PCR. Valid inference depends on accurate infection classification, similar enrolment and testing of symptomatic patients, and controls from the same source population as cases. The study uses a test-negative case-control design to evaluate real-world vaccine effectiveness.