Women should be tested for the Zika virus more than once during pregnancy as the pathogen can be intermittently present in the urine for up to seven months, researchers suggested.
The study showed that the test could again be positive for the Zika virus even after the viral load had disappeared in previous tests.
The virus can be detected in a patient's urine for as long as seven months.
"These results suggest the virus continues replicating during pregnancy, in the foetus or the placenta, which must serve as a reservoir for the pathogen," said Mauricio Lacerda Nogueira, Professor at the Sao Paulo Research Foundation (FAPESP) in Brazil.
"However, viral load in the mother's fluids is intermittent and very low, almost at the detection threshold," Nogueira added, in the paper appearing in the journal Emerging Infectious Diseases.
Molecular tests to detect Zika virus enable identification of the pathogen's genetic material in body fluids such as blood, urine, semen and saliva during the acute phase of infection.
These tests have also been used routinely in prenatal checkups for pregnant women with symptoms of the disease.
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.
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"We typically test urine samples because they are easier to obtain and because the blood viral load is lower and disappears faster," he said.
For the study, the team included women in different stages of pregnancy (four weeks to 38 weeks).
Some women had babies with complications -- such as hearing loss and brain cyst -- that were probably caused by Zika.
However, 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.
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