The U.S. Centers for Disease Control and Prevention said on Friday that some 157 pregnant women in the United States and another 122 in U.S. territories, primarily Puerto Rico, have tested positive for infection with the Zika virus.
The CDC, in a conference call, said that so far fewer than a dozen of the infected pregnant women it has tracked in the United States and Puerto Rico have had miscarriages or babies born with birth defects.
This was the first time the agency had disclosed the number of Zika-infected pregnant women in the United States and its territories.
According to Reuters, U.S. health officials have determined that the mosquito-borne virus, which can also be transmitted through unprotected sex with an infected person, can cause microcephaly, a birth defect marked by unusually small head size, and can lead to severe brain abnormalities and developmental problems in babies.
The agency told reporters on the call it has dramatically increased its testing capacity for Zika in the United States, as it girds for an increase in cases during the summer mosquito season.
Virtually all the Zika cases in the continental United States so far have been in people returning from countries where Zika is prevalent, such as Brazil, or through sexual transmission by travellers.
The latest report comes at a time when U.S. health officials have been clamouring for adequate funding to support mosquito protection and eradication, development of anti-Zika vaccines and better diagnostics and long-term studies needed to follow children born to infected mothers and to better understand the sexual transmission risk.