Brazilian health officials say the number of cases of microcephaly, a rare brain defect in babies, has risen to 3,893 since authorities began investigating the surge in cases in October.
Fewer than 150 such cases were seen in all of 2014. The Health Ministry has said the surge is linked to Zika virus, a mosquito-borne disease similar to dengue.
The ministry's emergency response official, Wanderson Oliveira, said most of the cases of microcephaly remain concentrated in Brazil's poor northeastern region.
However, the developed southeast where Rio de Janeiro and Sao Paulo are located is the second hardest-hit region. Oliviera spoke at a press conference today.
The US Centers for Disease Control and Prevention has issued an alert advising pregnant women to avoid travel to Latin American countries with Zika outbreaks.
