Repeat quantitative, reverse transcription polymerase chain reaction (RT-qPCR) testing in pregnant women with confirmed Zika virus infection showed that in some, the viral load in their urine disappeared and later returned (Emerg Infect Dis 2017;23:1891-3). These findings suggest a single negative test might not be sufficient to reassure women about their Zika status.

“These results suggest the virus continues replicating during pregnancy, in the fetus or the placenta, which must serve as a reservoir for the pathogen,” said the study’s senior author, Maurício Lacerda Nogueira, MD, PhD, a professor in the Medical School of São José do Rio Preto in São Paulo state, Brazil. “However, viral load in the mother’s fluids is intermittent and very low, almost at the detection threshold.”

Nogueira and his colleagues followed 13 pregnant women who were being treated at the Public Health Authority in São José do Rio Preto. The women were from 4-38 weeks pregnant at the time of enrollment and had positive viral RNA results via urine RT-qPCR, defined as cycle threshold ≤38.5. They had repeat RT-qPCR testing until they delivered their babies.

In five women, the researchers detected viruria after they had no detectible viral load in prior tests. One patient’s viruria persisted 7 months. In all the women, no viral load was detected after they delivered. This led the researchers to speculate that virus replication continues in fetal tissues like the placenta, umbilical cord, brain, liver, lung, and spleen. Three babies born to the study participants had complications that probably were Zika-related, including two with hearing loss and one with a brain cyst. The authors called for further research into understanding the meaning of this viruria and its consequences for newborns.