Aedes aegypti mosquito photographed through a microscope.
Over 150 pregnant women in the United States appear to have been infected with Zika virus. That's in addition to more than 120 women affected by Zika in U.S. territories, mainly Puerto Rico.
Those are the latest figures from the Centers for Disease Control and Prevention in Atlanta, which has been keeping track of all pregnant women in the U.S. and its territories who have lab tests suggestive of Zika virus infections.
So far, officials say they are aware of fewer than a dozen pregnancies that have had complications, although many of the pregnancies are ongoing. "We don't have full information yet on all of the outcomes," says Margaret Honein, chief of the CDC's birth defects branch.
Zika virus infection has been associated with miscarriage as well as birth defects like unusually small brains, called microcephaly. The exact risk posed by the virus remains unclear, and figuring that out is one reason the CDC is keeping track of affected pregnancies.
In the past, the CDC publicly reported on only those women who had both positive lab tests as well as symptoms. But officials say recent research suggests that women do not necessarily have to have symptoms to have their pregnancies affected. So the CDC is expanding its reporting to include women who didn't have symptoms.
"As the data accumulated about the risk of asymptomatic infections, it seemed more and more important to be very transparent and share publicly the numbers, the full number of pregnant women at risk of adverse outcomes associated with Zika," said Honein in a press briefing Friday.
Among the 157 pregnant women from U.S. states and the District of Columbia who are being monitored, only 49 percent reported symptoms consistent with Zika — mostly rash and fever.
Right now, CDC officials say they have no evidence that anyone has gotten Zika from being bitten by a mosquito in the continental United States. But public officials worry that this may eventually occur in places that have seen local transmission of other mosquito-borne disease, such as dengue.