It's official. The Zika virus has established a toehold in Florida.

Fourteen people likely caught Zika in a neighborhood north of downtown Miami, health officials said Monday. That means mosquitoes in that area have picked up the virus and are spreading it.

Zika can cause severe birth defects if a woman is infected at anytime during pregnancy.

So the Centers for Disease Control and Prevention is doing something it has never done before: issuing a travel advisory to a part of the continental U.S. because of an outbreak of an infectious disease.

Pregnant women should avoid travel to an approximately 1-square-mile area in the Wynwood Arts District of Miami, the CDC said Monday.

"We advise ... pregnant women who live and work in this area and their partners to make every effort to avoid mosquito bites and practice safe sex," said CDC Director Thomas Frieden.

If expectant mothers have been in the area anytime after June 15, they should be tested for Zika, Frieden added. Couples who have traveled to the affected area should wait at least eight weeks before trying to get pregnant.

Other doctors around the country are being even more cautious than the CDC.

Dr. Neil Silverman, an OBY-GYN at the University of California, Los Angeles, is advising pregnant women to avoid travel across two southern Florida counties: Miami-Dade County and Broward County.

"I think for now we need to be cautious, and I'm not sure in good faith could recommend a pregnant woman travel to that area of Florida right now," Silverman says. He adds that he plans to test all pregnant patients who have traveled to Miami-Dade and Broward counties for Zika.

Doctors at Baylor College of Medicine in Houston are considering expanding their travel advisory to all of Florida.

"There have been no official recommendation changes," said Dr. Martha Rac, an OB-GYN at Baylor in Houston. "I anticipate there will be travel warnings put out against all of Florida for pregnant women or for those attempting to become pregnant."

Frieden says the CDC limited its advisory to the small area where cases were found because the mosquito that spreads Zika — Aedes aegypti — can't fly very far.

"We can't predict the future, but we do know that the Aedes aegypti mosquito travels only about 150 meters [about 500 feet] maximum in its life," Frieden said. So he expects the current outbreak will be contained inside the small neighborhood.

Health officials have been trying to eliminate mosquitoes in the Wynwood neighborhood for weeks, but a "moderately high" number were still there Monday, Frieden says.

"In Miami, aggressive mosquito control effects don't seem to be working as well as we would have liked," he said.

But still, the chance of getting Zika around Miami is "very, very low," says Ashish Jha, who directs the Harvard Global Health Institute.

He thinks the CDC made the right decision by limiting the alert to just a small region.

"The CDC is walking a tightrope," Jha says. "Most people who go to southern Florida today are not going to be bitten by a mosquito that's infected," he says.

"You also don't want to create panic when you don't have the evidence that the disease is spreading elsewhere," Jha added.



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DAVID GREENE, HOST:

In Florida, health officials say Zika is being carried and spread by mosquitoes in a Miami neighborhood. They believe 14 people likely caught Zika in this area near downtown. Zika can cause severe birth defects if a woman is infected at any time during pregnancy. NPR's Michaeleen Doucleff reports on what this growing outbreak means for pregnant women throughout the U.S.

MICHAELEEN DOUCLEFF, BYLINE: For months now, Dr. Neil Silverman at the University of California, Los Angeles has been advising his pregnant patients and those trying to get pregnant not to travel to places where Zika is spreading. That includes countries in Central America, South America and the Caribbean. Now, Silverman says he's adding two counties in southern Florida to that list - Miami-Dade and Broward.

NEIL SILVERMAN: For the time being, I think that we have to be cautious. And I'm not sure I, in good faith, could recommend that a pregnant woman travel to that area of Florida right now.

DOUCLEFF: Silverman says he's treating these counties just like countries in Latin America. Pregnant women who have recently traveled there should get tested for Zika. And if a couple wants to get pregnant...

SILVERMAN: The current recommendations are that they wait for eight weeks to actively attempt to get pregnant. And that's both for men and for women.

DOUCLEFF: I talked to several doctors around the country, and they agreed with Silverman's assessment. Pregnant women shouldn't travel to the area around Miami. But the Centers for Disease Control and Prevention isn't going that far. It's limiting the travel advisory to just the small neighborhood in Miami where the Zika cases have been called the Wynwood art district. CDC's director, Dr. Thomas Frieden, says that's because the mosquito that spread Zika - Aedes aegypti - has a severe limitation.

THOMAS FRIEDEN: We can't predict the future, but we do know that the Aedes aegypti mosquito only travels about 150 metres maximum in its life.

DOUCLEFF: So he expects the outbreak to be contained inside the small neighborhood. Frieden says it's the first time the CDC has issued a travel alert for inside the continental U.S. due to an infectious disease. Ashish Jha at the Harvard Global Health Institute thinks the agency is making the right decision by limiting the alert to just a small region.

ASHISH JHA: Most people who go to southern Florida today are not going to be bitten by a mosquito that is infected with Zika. So for most people, the risk is very, very small. And you also don't want to create panic when you don't have the evidence that the disease is spreading elsewhere.

DOUCLEFF: But Jha does expect there to be more outbreaks in Florida besides this one in the Wynwood neighborhood.

JHA: My guess is that's where we started looking and that's where the first set of cases are, but there will probably be a lot more and probably much more widespread.

DOUCLEFF: If that happens, Frieden says the CDC will quickly expand the travel advisory to other parts of Florida. Michaeleen Doucleff, NPR News. Transcript provided by NPR, Copyright NPR.