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- CDC Recommends Repeat Testing to Verify Monkeypox
To prevent false positive test results, the Centers for Disease Control & Prevention (CDC) recommended on August 23 that laboratory professionals perform repeat testing to verify positive diagnostic results for orthopoxvirus or monkeypox virus DNA in specimens with high cycle threshold (Ct) values from persons who do not meet identified epidemiologic risk criteria for monkeypox.
The CDC recommended that laboratories review test results (including raw data, PCR curves, etc.) carefully before reporting the results. Since the molecular tests (eg, real-time PCR tests) are very sensitive, cross-contamination is possible.
If laboratories obtain a high Ct value (generally ~34 or higher), the CDC recommends to immediately re-extract and retest to ensure there was no cross-contamination. The CDC suggests this approach based on high Ct value alone, even in the absence of epidemiologic information. When possible, re-extract and re-test before you report results. Below are further CDC laboratory resources:
- Monkeypox Information for Laboratory Personnel
- How to Report Results from Orthopoxvirus, Non-Variola Orthopoxvirus, and Monkeypox Virus Laboratory Diagnostic Testing
- Laboratory Procedures and Biosafety Guidelines
- U.S. Monkeypox 2022: Situation Summary
- CDC Laboratory Outreach Communication System (LOCS)