Government health officials warned pregnant women Monday to avoid a Zika-stricken part of Miami, after the number of people feared infected through mosquito bites in the U.S. climbed to 14.

In its highly unusual and perhaps unprecedented travel warning, the Centers for Disease Control and Prevention also said expectant mothers should get tested for the virus if they have visited the neighborhood since mid-June.

All 14 cases are thought to have occurred in Miami’s Wynwood arts district, a trendy, fast-gentrifying neighborhood of warehouses, art galleries, restaurants and boutiques.

Florida Gov. Rick Scott asked for a CDC emergency response team to help the state combat Zika, which after sweeping Latin America and the Caribbean is beginning to spread in the U.S. The White House said a team will be sent quickly.

Health officials last Friday announced four cases of Zika that they believe are the first ones contracted from mosquitoes on the U.S. mainland. Ten more cases were announced Monday.

Zika infections in pregnant women can cause severe brain-related birth defects, including extremely small skulls. The outbreak has led to more than 1,800 serious defects.

CDC officials said they could not remember another time in the 70-year history of the agency when it told members of the public not to travel someplace in the U.S.

The travel warning covers an area of about one square mile in Wynwood to the east of Interstate 95 and south of I-195. It’s large enough, health officials said, to provide a buffer around the suspected hot zone. The tropical mosquito that spreads Zika travels less than 200 yards in its lifetime.

Some experts said that’s far too small a radius. Dr. Peter Hotez, a tropical medicine expert at the Baylor College of Medicine in Texas, said the CDC should be more cautious and expand the travel advisory to all of Miami-Dade County.

“If you’re pregnant or think you might be pregnant, avoid travel to Miami, and possible elsewhere in South Florida,” he said. “I’m guessing most women who are pregnant are doing that. I don’t think they’re sitting around for the CDC to split hairs and fine-tune it to a specific area.”

CDC Director Dr. Tom Frieden said the narrowly drawn warning was dictated by science and not by any concern for Florida’s crucial tourism industry. He said it was based on the nation’s ability to contain outbreaks of other diseases carried by the same mosquito.

“There wouldn’t be a technical or scientific basis to give a broader recommendation,” Frieden said.

U.S. health officials have said all along that while isolated clusters of Zika may occur in this country, they do not expect major outbreaks like those seen in Latin America, because of better sanitation and mosquito control and widespread use of air conditioners and window screens.

At the same time, health officials expressed concern that they continue to see “moderately high” numbers of the Zika-carrying mosquito in the area, despite aggressive use of insecticides.

“This is a very difficult mosquito to control,” Frieden said.

Florida health officials said they have tested more than 200 people in Miami-Dade and Broward Counties since early July. The CDC emergency team will help Florida officials investigate the outbreak, collect samples and control mosquitoes.

Of the 14 people infected, two are women and 12 are men. Eight patients showed symptoms of Zika, which can include fever, rash, joint pain and red eyes. The others had no symptoms. The disease is often so mild that most people don’t know they are infected.

“We will continue to keep our residents and visitors safe utilizing constant surveillance and aggressive strategies, such as increased mosquito spraying, that have allowed our state to fight similar viruses,” the governor said in a statement.

(AP)