A nursing home resident had vomiting and diarrhea from norovirus that resolved completely 10 days ago. Repeat stool RT-PCR for outbreak clearance testing is still positive. What is the correct interpretation?
- A The patient has relapsed and must remain in strict isolation indefinitely
- B The positive result proves a false negative initial diagnosis
- C Norovirus RNA can be shed in stool for weeks after clinical recovery, so a positive PCR does not necessarily indicate infectiousness ✓
- D Stool PCR should never be used for norovirus because it detects only dead virus
Correct answer: C. Norovirus RNA can be shed in stool for weeks after clinical recovery, so a positive PCR does not necessarily indicate infectiousness
Explanation
Norovirus RNA shedding commonly continues for 2 to 3 weeks or longer after symptom resolution, and sensitive RT-PCR readily detects this residual RNA. Prolonged shedding does not equate to ongoing infectiousness, and clearance testing by PCR is therefore unhelpful. Isolation decisions rest on symptom status. The original diagnosis stands, and PCR detects viral RNA irrespective of viability, though its extreme sensitivity is exactly why it stays positive late.
Reference: Koneman's Color Atlas and Textbook of Diagnostic Microbiology, 7th ed.
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