On May 15, 2015, Zika virus circulation was confirmed in Brazil, and the Centers for Disease Control and Prevention (CDC) subsequently activated its Emergency Operations Center and responded to the Zika virus outbreak in the Americas and U.S. Territories. Between May 15 and December 15, 2016, a total of 707,133 autochthonous Zika virus cases were reported in the Region of the Americas.

Because of ongoing Zika virus transmission, the occurrence of associated complications, and the risk for recurrence of large outbreaks, countries where Aedes mosquitoes were present should continue surveillance for Zika virus disease, GBS, and congenital abnormalities.

As of December 15, 2016, increases in the number of GBS cases had been reported in 13 countries and territories with documented Zika virus transmission, compared with baseline data. Six additional countries and territories reported laboratory confirmation of Zika virus infection in at least one GBS patient. The temporal trend in reported GBS cases in the 19 countries has largely paralleled that of Zika virus disease cases. Although congenital microcephaly and other neurologic abnormalities have been reported among infants born to mothers who were infected with Zika virus during pregnancy, variable reporting of congenital Zika virus syndrome did not permit a comparison of trends in reported congenital abnormalities within the region.