Microcephaly in South Brazil: Are cases of Congenital Zika Syndrome increasing in recent years?

Northeast Brazil was the first region to detect a significant increase in babies born with microcephaly associated with prenatal zika virus infection in 2015. Rio Grande do Sul (RS) state was less impacted due to the temperate climate preventing the spread of the vector. This study investigated the prevalence and etiology of congenital microcephaly in RS in two different periods. This cross-sectional descriptive study included all live births with congenital microcephaly in RS from 2015 to 2022. Cases were divided into two groups: P1 "outbreak" (2015-16); and P2 "endemic" (2017-22). There were 58 cases of microcephaly (3.8/10,000) in P1 and 148 (1.97/10,000) in P2. Congenital Zika Virus infection was the etiology in 5.2% (n=3) in P1 and 6.7% (n=10) in P2. In conclusion, although the ZIKV outbreak in Brazil has receded, RS remains an area of concern, with a possible slight increase of live births with microcephaly secondary to ZIKV prenatal infection relative to the number of cases due to congenital infections. The broader distribution of the vector Aedes aegypti with warmer temperatures in our state might be linked to the increase in recent years. This study can be an alert to other regions of temperate or subtropical climates.