Moms-to-be should be tested more than once for Zika

When it comes to testing moms-to-be for the presence of Zika, a single negative result may not be enough.

"We monitored a group of pregnant women with a confirmed diagnosis of Zika and tested their urine over a period of several months at intervals of about a week. In some of these women, the viral load in their urine disappeared and later returned," said principal investigator Maurício Lacerda Nogueira from the FAMERP - Medical School of Sao Jose do Rio Preto, Sao Paulo State.

The patients included 13 women in different stages of pregnancy (4 weeks to 38 weeks) who were receiving treatment at the Children's & Maternity Hospital (HCM) of Sao Jose do Rio Preto.

According to Nogueira, the virus was detected in one patient's urine for as long as seven months. In five women, the test was again positive for Zika virus after their viral load had disappeared in previous tests. In all cases, the virus vanished from the women shortly after they gave birth.

"These results suggest the virus continues replicating during pregnancy, in the fetus or the placenta, which must serve as a reservoir for the pathogen," Nogueira said. "However, viral load in the mother's fluids is intermittent and very low, almost at the detection threshold."

According to Nogueira, if the result of a molecular test is negative, it should ideally be repeated at least twice at intervals of no less than a week.

"We typically test urine samples because they're easier to obtain and because the blood viral load is lower and disappears faster," he said.

Three of the women monitored for the study had babies with complications that were probably caused by Zika: two displayed hearing loss and one was born with a brain cyst.

The researchers were unable to establish a correlation between the number of times the virus was detected in the mother and the occurrence of an adverse outcome. "To do so, we will need to perform new studies with a larger number of participants," Nogueira said.

The results are published in the journal Emerging Infectious Diseases.