The Centers for Disease Control and Prevention has issued its first travel advisory warning for a part of the continental U.S., warning pregnant women to avoid travel to the Miami-Dade County area after Florida health officials reported 14 locally transmitted cases of the Zika virus.
CDC Director Dr. Tom Frieden said the warning was prompted by largely ineffective efforts to control the population of the virus' primary carrier—the Aedes aegypti mosquito.
“It appeared that the mosquito control activities hadn't had the level of success that we had hoped,” Frieden said during a call with reporters on Monday. “They're still seeing more Aedes aegypti mosquitoes than we had hoped.”
Frieden said pregnant women as well as women who are considering pregnancy should avoid unnecessary travel to the impacted area, which Florida officials identified as a one-square mile radius just north of downtown Miami.
Frieden broadened the area to about150 meters. Unlike other mosquito types, the Aedes aegypti flies a relatively short distance and prefers residential areas. It can travel an average of 400 meters throughout its lifetime, according to the World Health Organization, which means the virus could spread more by human travel.
Some experts say the travel warning area is too small. 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 possibly 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."
Zika infections in pregnant women can cause severe brain-related birth defects. The outbreak has led to more than 1,800 cases of microcephaly, in which a baby is born with an extremely small head.
Florida Gov. Rick Scott released a statement Monday saying the state remained safe for tourists, adding 30 million have visited this year.
“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,” Scott said. “While I encourage all residents and visitors to continue to use precaution by draining standing water and wearing bug spray, Florida remains safe and open for business.”
More than 2,300 people throughout Florida have been tested for Zika, according to state health officials. Since July 7, more than 200 individuals in Miami-Dade and Broward counties who live or work near the 14 confirmed cases—12 men and two women—have been tested for the virus.
Among them, six had no symptoms and were identified through a door-to-door community outreach campaign, officials said.
It is not known why efforts to control the Aedes aegypti mosquito population have failed. Frieden said members of the CDC's Emergency Response Team were already on the ground with more staff expected to arrive in the next day. They will assist state health officials with monitoring and tracking the virus as well as with mosquito abatement.
The Associated Press contributed to this report.