Zika RNA can linger in semen for up to 3 months, but clears from vaginal fluid almost immediately, according to interim results from the first prospective study of patients infected with the virus.
"These findings support the CDC recommendations for men to abstain from sex or use condoms for 6 months," said investigator Gabriela Paz-Bailey, MD, PhD, from the Centers for Disease Control and Prevention.
Doctors should also ask pregnant women "about travel to areas where there is active transmission and offer testing," she told Medscape Medical News.
The CDC issued guidance for physicians on Zika testing and prevention in July 2016, but the basis for that instruction was best guesses and individual case reports. Officials were "really operating in the dark," Dr Paz-Bailey explained.
To determine the persistence of the Zika virus in bodily fluids, Dr Paz-Bailey and her colleagues identified 150 residents of Puerto Rico — 66 women and 84 men — using a pre-existing arboviral reporting system. The team followed the participants from the first report of symptoms or diagnosis, and collected saliva, urine, blood serum, semen, and vaginal secretions at baseline and at 2, 4, and 6 months.
Dr Paz-Bailey presented the results here at the Conference on Retroviruses and Opportunistic Infections 2017. A preliminary report of the data was published online in the New England Journal of Medicine to coincide with the presentation.
Viral Particles in Bodily Fluid
The duration of viral particles varied by bodily fluid. Only one vaginal swab came back positive for Zika RNA during the 6-month study, putting vaginal fluid on par with saliva for Zika persistence.
However, half the semen samples tested positive for Zika particles at 1 month, and 5% tested positive at 81 days. In previous case reports, Zika has been documented in the semen of two men at 6 months.
There were also surprises in blood samples. Half showed the presence of Zika RNA in blood serum 2 weeks after the start of symptoms, and 5% showed that presence at 54 days.
In urine, however, the virus was less persistent. Zika particles were detected in half the samples at 1 week, and in 5% at 39 days.
"These findings suggest that serum may be better for diagnosing Zika virus," said Dr Paz-Bailey.
This differs from previous findings, which suggested that Zika lingers longer in urine than in blood serum. But that difference could be related to the prospective nature of the study by the CDC team. Cross-sectional and incident studies "are not designed to look at duration," Dr Paz-Bailey pointed out.
Still, the findings were a surprise to David Thomas, MD, from the Johns Hopkins University School of Medicine in Baltimore. Usually, it's the urine where viruses persist the longest, he explained.
"I think that's something that will need to be verified," he told Medscape Medical News. "I don't think that's a critical part of the abstract, though. The CDC recommendations are continuing to be verified. I think that's the take-home message."
Persistence and Infectiousness
These data are important because they suggest how long a person can remain infectious. However, it's too soon to know. After all, RNA fragments can persist for a long time without the capacity to infect another person, said Dr Paz-Bailey.
She said she expects that the final readout of the data — which the researchers hope will include 300 people — will provide evidence to guide clinical practice. Once they have that, Dr Paz-Bailey said she and the team will re-do the analysis to see if anything has changed.
"It's taken many years of HIV research to determine what amount of virus is needed to result in transmission," she told Medscape Medical News. "In Zika, there are still so many unknowns."
This study was funded by the Centers for Disease Control and Prevention. Staffing support was provided by the Center for AIDS Research at Emory University. Dr Paz-Bailey and Dr Thomas have disclosed no relevant financial relationships.
Conference on Retroviruses and Opportunistic Infections (CROI) 2017: Poster 1055LB. Presented February 14, 2017.