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CDC recommends testing urine samples for Zika virus
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The CDC updated its diagnostic testing guidance for Zika virus after discovering that Zika RNA can be detected at higher levels and for a longer duration in urine samples than serum samples, according to a recent MMWR.
“Results of testing conducted at [the Florida Department of Health Bureau of Public Health Laboratories (BPHL)] suggest that urine might be the preferred specimen type to identify acute Zika virus disease,” Andrea M. Bingham, PhD, researcher at Florida’s health department, and colleagues wrote. “Rates of detection from urine were higher than from serum, even during the first few days after symptom onset and continuing after day 5, when no serum specimens tested in this evaluation had detectable RNA.”
Bingham and colleagues performed real-time reverse-transcription PCR on urine specimens collected from 70 patients with Zika virus disease. Viral RNA was detected in 65 samples that were collected between 1 and 20 days after symptom onset.
Testing on both urine and serum specimens collected from 66 patients, including two pregnant women, showed that nearly twice as many patients had detectable levels of Zika virus in their urine samples vs. serum samples (92% vs. 47%). Among the 55 patients with specimens collected during the first 5 days after symptom onset, 95% had detectable viral loads in their urine vs. 56% with detectable loads in serum. Among the remaining 11 patients whose samples were collected more than 5 days after symptom onset, 82% had positive urine specimens, and none had positive serum specimens.
In addition to urine and serum samples, saliva samples also were available for 53 patients. Testing revealed that Zika RNA was present in 92% of urine samples, 81% of saliva samples and 51% of serum samples. Although viral RNA was detected in saliva up to 20 days after symptom onset, no patients had detectable loads in saliva samples alone.
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Based on these findings, the CDC now recommends that diagnostic testing for Zika virus be performed on urine specimens collected from suspected cases no more than 14 days after symptom onset, and in conjunction with serum samples collected less than 7 days after symptom onset. The agency will continue to review its guidance and update its recommendations as new data emerges.
“The ability to confirm that a recent illness is caused by Zika virus and not another flavivirus by detection of Zika virus RNA in a clinical specimen is important, given the limitations in interpretation of results from serology testing in persons who have had previous flavivirus infection or vaccination,” Bingham and colleagues concluded. “Among pregnant women, this ability to confirm Zika virus is important because close monitoring during pregnancy is recommended for women with confirmed Zika virus disease.” – by Stephanie Viguers
Disclosure: The researchers report no relevant financial disclosures.
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