BACKGROUND: Identifying pregnant women with possible Zika virus (ZIKV) infection facilitates timely identification of infants potentially exposed to ZIKV in utero.
METHODS: Since February 2016, the New York City Department of Health and Mental Hygiene (NYCDOHMH) has been investigating cases of possible ZIKV infection in exposed pregnant women and their infants. Cases were identified by (1)laboratory evidence of recent ZIKV infection in maternal and/or fetal/infant specimens, and/or (2)provider report of prenatal/postnatal findings potentially consistent with congenital ZIKV. Confirmed cases had a positive/equivocal result on ZIKV nucleic acid amplification testing (NAAT), or a positive/equivocal result on ZIKV immunoglobulin M (IgM) with a serum plaque reduction neutralization testing (PRNT) titer ≥10 for ZIKV and <10 for other flaviviruses. Probable cases had a positive/equivocal IgM with PRNT titers ≥10 for both ZIKV and another flavivirus. Through provider and patient interviews and chart review, we collected information on risk exposure, clinical course, imaging, pregnancy outcome (i.e., live birth, elective/spontaneous pregnancy loss), and infant assessment.
RESULTS: As of December 23, 2016, 332 pregnant women in NYC had laboratory evidence of recent ZIKV infection, among whom 251 (76%) had completed pregnancies, with 227 (90%) live infants and 24 (10%) pregnancy losses. These outcomes occurred among 70 confirmed and 181 probable ZIKV cases in pregnant women. Twenty of 227 (9%) infants had laboratory evidence of recent ZIKV infection; one infant had a positive result on urine NAAT, and all 20 infants had an equivocal/positive result on IgM. Five of 227 (2%) infants had congenital Zika syndrome (CZS), with microcephaly and intracranial abnormalities. Notably, the mothers of three infants with CZS tested negative on NAAT and IgM, though all three mothers had positive PRNT titers for ZIKV and dengue; these cases were tested >12 weeks after earliest possible exposure, and were reported to NYCDOHMH because of prenatal/postnatal findings compatible with CZS. One mother of an infant with CZS had no ZIKV testing and the other was a probable ZIKV case. Two of 15 infants with laboratory evidence of ZIKV but without CZS had abnormal results on hearing evaluation by auditory brainstem response.
CONCLUSIONS: Among infants born to women with possible ZIKV infection during pregnancy, 9% had laboratory evidence of ZIKV, and 2% had CZS. Negative maternal ZIKV results cannot rule out infection for women tested >3 months after exposure. Consequently, provider awareness and reporting of concerning prenatal/postnatal findings are essential to ensure identification of infants with congenital ZIKV infection.