Zika virus vertical transmission in children with confirmed antenatal exposure

BackgroundIn utero transmission of Zika virus (ZIKV) can lead to adverse infant outcomes, but vertical transmission rates are unknown.MethodsAntenatally ZIKV-exposed children were followed prospectively since the time of the Rio de Janeiro epidemic in 2015-16. Serum and urine specimens were collected from infants from birth throughout the first year of life. Specimens were tested by quantitative reverse transcriptase polymerase chain reaction (PCR) and/or IgM antibody capture Zika MAC-ELISA. Infants had neurodevelopmental evaluations, brain imaging, eye examinations, and hearing assessments.ResultsOver time 130 in utero ZIKV-exposed (mothers PCR+) children were tested with 407 specimens evaluated: 161 sera were tested by PCR and IgM assays, 85 urines by PCR; 84 children (65%) were positive in at least one assay. Among 94 children tested within 3 months of age, 70% were positive (39% serum PCR, 48% urine PCR, 39% IgM). After 3 months, 33% were positive by any laboratory method. Five children were intermittently PCR+ beyond 200 days of life. Concordance between IgM and PCR results was 52%, sensitivity 65%, specificity 40% (with any positive PCR result as the gold standard); IgM and serum PCR were 61% concordant; serum and urine PCR 55%. Most children (65%) were clinically normal. Positive results were seen in 29 of 45 children (64%) with abnormal findings and 55 of 85 normal children (65%), p=0·98. Earlier maternal trimester of infection was associated with positive infant laboratory results but not infant clinical disease (p=0·04).ConclusionsZIKV has a high in utero transmission rate. Laboratory confirmed infection is not necessarily associated with abnormal infant findings.