What is the role of confirmatory laboratory testing in an outbreak investigation, and how should discordant results be handled?

• A. Laboratory results are unnecessary for case definitions.
• B. Initial tests are sufficient; discordant results are ignored.
• C. Discordant results require repeat testing, clinical correlation, and possibly alternative assays.
• D. Confirmatory tests establish true case status; discordant results require repeat testing, clinical correlation, and possibly alternative assays.

Answer: (D)

Confirmatory laboratory testing is used to certify case status with high specificity in an outbreak, so the count of true infections is accurate and reliable for guiding control actions. Initial tests are important for rapid screening, but they can yield false positives or miss low-level infections; confirmation helps prevent misclassification that could misdirect resources or actions. When results don’t align, the correct approach is to pursue repeat testing, ideally with a different assay or platform, and to obtain a new specimen if needed. Always interpret discordant results in the context of clinical presentation and epidemiologic links—symptoms, exposure history, and known contacts can tip the balance toward true infection even if one result is inconclusive. Depending on the situation, use alternative assays that target different pathogen components or methods to resolve the disagreement. Document and integrate discordant findings into the investigation to refine case status and inform outbreak response.