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Zika PCR Testing Guidance Updated by CDC

NEW YORK (GenomeWeb) – The US Centers for Diseases Control and Prevention has updated its guidance for molecular Zika testing based on a recent analysis of different sample types, recommending more testing of urine.

Published today in a Morbidity and Mortality Weekly Report, the analysis compared sample types from 70 travel-associated cases in Florida tested since April 20. It found that about twice as many urine samples tested positive using a lab-developed Zika PCR compared to serum samples. 

The agency noted that the RT-qPCR assay used was a previously published assay from Lanciotti et al., rather than the CDC's Triloplex test, which was granted emergency-use authorization. Among the 66 samples of urine and blood serum collected on the same day, 61 urine samples tested with the Lanciotti assay came back positive, while only 31 serum samples did. 

For 55 samples tested in the zero to five-day range after symptom onset, 95 percent of urine samples tested positive while only 56 percent of serum samples did. And eight of nine urine samples tested in the six to 10 day-range were positive, but none of the serum samples were.

A second evaluation compared urine, serum, and saliva collected on the same day from a subset of 53 patients with Zika virus infection, at varying times after symptom onset. It showed positive results in 49 urine specimens and 43 saliva specimens, but only 27 serum specimens.

In this particular analysis, all seven samples tested one day after symptom onset were positive in both urine and saliva, but only six out of seven, or 86 percent, were positive in serum. Nine sets of samples were evaluated two days after onset, and all were positive in urine and saliva, while only six out of nine, or 67 percent, were positive using serum.

The MMWR report highlighted the fact that Zika virus RNA was detectable in urine as early as the first day of symptoms and, in one case, as late as 20 days after onset.

Based on this data, the CDC issued new guidelines for Zika testing, recommending RT-qPCR be performed on urine collected less than 14 days after onset of symptoms in patients with suspected Zika virus disease. Less than seven days after onset, urine should be tested in conjunction with serum.

The agency also noted that the CDC Trioplex rRT-PCR test is the only assay authorized by the US Food and Drug Administration for testing of urine. According to the interim guidance statement, other laboratory-developed tests will need in-house validations to adequately characterize the performance of different assays on urine, and will have to meet CLIA requirements.