More than 3,100 pregnant Colombian women are infected with the mosquito-borne Zika virus, President Juan Manuel Santos said on Saturday, as the disease continues its rapid spread across the Americas.

Brazil is investigating the potential link between Zika infections and more than 4,000 suspected cases of microcephaly, a birth defect marked by an abnormally small head size that can result in developmental problems. Researchers have identified evidence of Zika infection in 17 of these cases, either in the baby or in the mother, but have not confirmed that Zika can cause microcephaly.

There are so far no recorded cases of Zika-linked microcephaly in Colombia, Santos said. The government is now uncertain about a previous projection for up to 500 cases of Zika-linked microcephaly, based on data from other countries battling the disease, he said.