Low prevalence after the first Zika virus epidemic wave in Southeastern Brazil

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Background: Zika virus (ZIKV) emerged in Brazil in 2014. One year later its teratogenic effect was noticed in Northeastern Brazil and elsewhere. With the aim to determine the seroprevalence of ZIKV antibodies among parturient women, the incidence of ZIKV infection among the newborns, the risk of transmission from an infected mother to the newborn, the incidence of congenital anomalies among the infected babies, and the dynamics of viral excretion in breastmilk and urine, a cohort study was set up at Hospital Ana Costa (HAC), a private institution, located in Santos, Southeastern Brazil. Methods & Materials: Women who came to HAC for delivery were invited to participate. The ones who agreed to participate signed the Informed Consent Form. The study was approved by the USP Medical School Ethics Review Board. A blood sample was collected for the woman serology. After delivery, samples of colostrum and breastmilk were obtained, as well as a sample of cordblood and urine of the newborn for PCR. EIA for ZIKV antibodies was carried out. Positive samples were confirmed by flow cytometry neutralization test (FRNT). Results: From June 2016 to February 2017 a total of 740 parturient women and their 753 newborns were enrolled in the study. ZIKV seroprevalence among the women was 7.2% (53/740). No infected newborns nor any ZIKV-related congenital anomalies were observed. Seroprevalence was higher among women living in two of the Santos metropolitan region cities, as compared to the others. Seroprevalence was not related to the mothers’ age, to the duration of pregnancy, to the referral of ZIKV-like symptoms during pregnancy, nor to the referral of family members or neighbors with ZIKV-like symptoms during pregnancy. The only variable significantly associated with seroprevalence was a previous history of dengue. Conclusion: ZIKV seroprevalence among parturient women in Santos metropolitan region after the first epidemic wave was low, and no mother to baby transmission was observed. The region is endemic for dengue. Since its emergence in 1997 eight large outbreaks were reported. 2017 is being characterized as a low transmission year for dengue and ZIKV in Brazil. New ZIKV outbreaks should be expected in the future. Grant FAPESP no.2016/16069-8