The virus is spread through mosquito bites and typically causes fever, rash, joint pain and red eyes, said Dr. Lyle Peterson, director of the CDC’s division of vector borne disease. The illness is typically mild and can present symptoms for as long as one week.
"Brazil has been combating a large outbreak of Zika since last year," Peterson said. "Officials there have noted a rather significant increase in cases of microcephaly."
>> Read more trending stories
Scientists with the CDC said Friday they tested samples from two pregnancies that ended in miscarriages and from two infants diagnosed with microcephaly who died shortly after birth in Brazil.
"They determined that all four cases were positive for Zika virus infection, indicating that the babies had become infected during pregnancy," Peterson said.
Authorities in Hawaii sent samples to the CDC from the child born in Oahu with microcephaly after "an astute Hawaii physician recognized the possible role of Zika virus infection," according to the state Department of Health.
On Friday, the CDC released an interim travel advisory warning pregnant women to postpone travel to areas where Zika virus transmission is ongoing. The countries include Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname and Venezuela, as well as Puerto Rico.
It was not immediately clear how likely the virus was to spread to the U.S.
"Many areas of the United States have mosquitoes that can become infected with and transmit Zika virus," Peterson said. "However, recent chikungunya and dengue outbreaks in the United States suggest that Zika outbreaks in the U.S. mainland may be relatively small and focal."
According to the CDC, doctors first saw the Zika virus in U.S. travelers in 2007. From then until 2014, the CDC noted a total of 14 returning U.S. travelers suffered from the illness. Scientists continued to test samples from travelers who became ill in 2015 and 2016 but so far have identified 12 Americans who caught the virus abroad.