Increase in Reported Prevalence of Microcephaly in Infants Born to Women Living in Areas with Confirmed Zika Virus Transmission During the First Trimester of Pregnancy — Brazil, 2015

What is already known about this topic? An outbreak of Zika virus disease caused by a flavivirus transmitted by Aedes mosquitoes occurred in Brazil in early 2015. An increase in the prevalence of infants born with microcephaly has been reported in Brazil since October 2015 in association with clusters of febrile rash illness in pregnant women. What is added by this report? The birth prevalence of microcephaly in Brazil increased sharply during 2015-2016. The largest increase occurred in the Northeast region where Zika virus transmission was first reported in Brazil. This analysis of 574 cases of microcephaly detected through a newly established ad hoc microcephaly surveillance system identified temporal and geospatial evidence linking the occurrence of febrile rash illness consistent with Zika virus disease during the first trimester of pregnancy with the increased birth prevalence of microcephaly. The prevalence of microcephaly in 15 states with laboratory-confirmed Zika virus transmission (2.8 cases per 10000 live births) significantly exceeded that in four states without confirmed Zika virus transmission (0.6 per 10000). What are the implications for public health practice? The suggested link between maternal exposure to Zika virus infection during the first trimester of pregnancy and the increased birth prevalence of microcephaly provide additional evidence for congenital infection with Zika virus. Ongoing surveillance is needed to identify additional cases and to fully elucidate the clinical spectrum of illness. Pregnant women should protect themselves from mosquito bites by wearing protective clothing applying insect repellents and when indoors ensuring that rooms are protected with screens or mosquito nets.