Study Identifies Urine as Preferred Zika Sample

Diagnosing Zika virus is challenging. While diagnosis previously relied on serology, it is difficult to differentiate Zika antibodies from other closely related viruses, including dengue. As a result, the World Health Organization (WHO) has encouraged test developers to move away from serology-based assays towards nucleic acid-based assays that are more specific and sensitive, if performed during the acute phase of infection. But, new evidence shows that the sensitivity of nucleic acid testing can be impacted by sample type.

Test developers around the world are working to quickly deploy tests for surveillance, clinical diagnosis and monitoring, and blood donation screening. Diagnostic Testing & Emerging Technologies (DTET) undertook a sampling of evolving testing recommendations, federal efforts to speed diagnostic development, and industry’s progress on bringing tests to market as the Southern sections of the United States brace for mosquito season and potential local Zika transmission.

Significant development efforts are underway for improved molecular and serologic assays for detection of Zika infection. In addition to clinical diagnostics, assays are in development for blood, organ, and tissue donor screening.

“Nucleic acid testing is moving forward well with extremely high sensitivity and throughput, development efforts are very successful,” Michael Busch, M.D., Ph.D., co-director of the Blood Systems Research Institute in San Francisco, told DTET.

In an interim guidance published May 13 in Morbidity and Mortality Weekly Report, the CDC says that real-time reverse transcription–polymerase chain reaction (rRT-PCR) is the preferred test for Zika virus infection because of its rapid turnaround and its high specificity. However, given emerging information, urine samples may be preferable to serum depending on the length of time from onset of symptoms.

Zika virus RNA is unlikely to be detected in serum after the first week of illness, but Zika virus RNA can be detected in urine for at least two weeks after onset of symptoms, the CDC says. Therefore, CDC recommends that Zika virus rRT-PCR be performed on urine collected less than 14 days after onset of symptoms in suspected patients and that rRT-PCR urine testing be performed in conjunction with serum testing if specimens are collected less than seven days after symptom onset.

This recommendation was based on findings of a Florida Department of Health study of multiple specimen types from persons with suspected Zika virus disease. Test results were classified by specimen type and number of days after symptom onset to determine the most sensitive and efficient testing algorithm for acute Zika infection. Results were published May 10 in Morbidity and Mortality Weekly Report. For more detailed discussion of the study and of test development efforts underway, see the June issue of Diagnostic Testing & Emerging Technologies.