The government on Wednesday recommended Zika testing for all pregnant women who recently spent time anywhere in Florida's Miami-Dade County.
The county is the only area in the continental U.S. where mosquitoes have been spreading the virus since the summer. Testing is recommended for pregnant women who lived in — or visited — Miami-Dade since August 1, whether or not they have symptoms.
The Centers for Disease Control and Prevention had previously urged testing for pregnant women who had been in one of the county's Zika "hot zones." On Wednesday, it extended the advice to the entire county.
New cases continue to come in from the Miami area "and we want to be cautious," said the CDC's Dr. Denise Jamieson. There have been more than 150 Zika cases in the county blamed on local mosquitoes.
Zika is mainly spread by mosquitoes, but can be spread through sex. Most infected people don't get sick. It can cause a mild illness, with fever, rash and joint pain. But infection during pregnancy can lead to severe brain-related birth defects.
The new testing advice also extends to pregnant women who weren't in Miami-Dade themselves, but had unprotected sex with someone who had been in the county recently.
The advice for travel to Miami-Dade has not changed: Pregnant women should postpone travel to the county if possible and stay out of the two remaining "red zones" — Miami Beach and an area just north of the Little Haiti neighborhood.
Until this summer, the only cases of Zika in the continental U.S. were connected to travel to areas with Zika epidemics, mostly the Caribbean and Latin America. Of the more than 3,900 cases to date, nearly 900 were pregnant women.
Dr. Neil Silverman, a UCLA professor of obstetrics, said doctors are probably already taking precautions with their patients who traveled to the Florida county.
Beginning in July, "I started treating Miami-Dade County like Brazil," said Silverman, who's been advising California health officials on Zika issues. "If a patient had been anywhere in the Miami area, I offered testing."