New data showing that Zika virus can be found at higher levels or for longer duration in urine than serum, has prompted the Centers for Disease Control and Prevention to update its interim diagnostic testing guidance for the virus in public health laboratories.
The CDC now recommends that Zika virus real-time reverse transcription–polymerase chain reaction (rRT-PCR) be performed on urine collected less than 14 days after the onset of symptoms in patients with suspected Zika virus disease. The rRT-PCR is the preferred test for Zika infection because it can be performed rapidly and is highly specific, the CDC notes, and currently, the CDC Trioplex rRT-PCR assay is the only diagnostic tool authorized by the Food and Drug Administration for Zika virus testing of urine (MMWR. 2016 May 10. doi:10.15585/mmwr.mm6518e1).
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In most patients, Zika virus RNA is unlikely to be detected in serum after the first week of illness, the CDC said, but adaptations of previously published diagnostic methods suggest that Zika virus RNA can be detected in urine for at least 2 weeks after onset of symptoms. However, the CDC affirmed that Zika virus rRT-PCR testing of urine should be performed in conjunction with serum testing if using specimens collected less than 7 days after symptom onset, and a positive result in either specimen type provides evidence of Zika virus infection.
The CDC added that, because viremia decreases over time and dates of illness onset may not be accurately reported, a negative rRT-PCR does not exclude Zika virus infection, and IgM antibody testing should be performed. The agency also said other laboratory-developed tests will need in-house validations to adequately characterize the performance of the assay and meet Clinical Laboratory Improvement Amendments requirements.
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