The World Health Organization on Feb. 1 declared the Zika virus outbreak to be a global public health emergency, citing a "strongly suspected" relationship between Zika infection in pregnancy and microcephaly.
Zika has not been proven to cause microcephaly in babies, but there is growing evidence that suggests a link. The condition is defined by unusually small heads that can result in developmental problems.
Brazil said it has confirmed more than 860 cases of microcephaly, and considers most of them to be related to Zika infections in the mothers. Brazil is investigating more than 4,200 additional suspected cases of microcephaly.