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CDC issues travel warning as Zika cases rise in Florida. Here’s what you need to know.

The number of Zika virus infections in Florida is on the rise.

On Monday, Florida Gov. Rick Scott announced that a total of 14 people (12 men and two women) are believed to have contracted the virus in the state. This is up from the four infections reported last week by the Florida Department of Health and Centers for Disease Control and Prevention, an announcement that signaled local mosquitoes are likely now transmitting the virus.

Health officials say Zika is currently limited to just a one-square-mile area north of downtown Miami. As a precaution, the CDC issued a travel warning for women who are or are thinking are becoming pregnant against traveling to the affected area.

"Because mosquito control efforts in this specific community ... don’t appear to be working as well as we as we would have hoped, and because we have seen more Zika cases over a longer time frame, we advise pregnant women to avoid travel to this area and pregnant women who live or work in this area to make every effort to avoid mosquito bites," Tom Frieden, the CDC director, said Monday.

Frieden added that it’s believed 12 of the 14 cases originated from a very small 150-square-meter area, and that the people contracted the virus while at work. Mosquito control has been difficult in this area, he said, due to a few reasons:

  • The mosquitoes may have become resistant to insecticides.
  • The breeding sites have been very hard to find in the urban environment
  • The Aedes aegypti mosquitoes that transmit the virus are very difficult to control.

"Despite the daily use of spraying, the vector control experts there are seeing new larval mosquitos, and moderately high Aedes aegypti counts," Frieden said.

Overall, the uptick isn’t shocking, and is partially the result of health investigators doing more surveillance. The Florida Department of Heath has been conducting door-to-door surveys, testing people for the virus, the Washington Post reports.

It’s also in line with what the CDC has been predicting for months: a small, but controllable, outbreak of Zika in the southeastern United States.

"At this time, the department believes that active transmission of the Zika virus [is] occurring in one small area in Miami-Dade County, just north of downtown," the Florida Department of Health reports.
Florida Department of Health

"We would not be surprised if additional cases are reported," Frieden told reporters on Friday. "In fact, there will be more cases we’re not aware of right now, because most people infected with Zika don’t have symptoms. People infected several weeks ago may also have their infections diagnosed as we do, and as Florida does community surveys in the area."

Gov. Scott said that the state has requested additional resources from the CDC for an emergency response. (Frieden told reporters Monday such a response team is on the way.)

Scott is also confident the health agencies will be able to prevent Zika from spreading into a major outbreak. "Florida has a proven track record of success when it comes to managing similar mosquito-borne viruses," he said in a statement.

The state has managed to control several small outbreaks of chikungunya fever, another virus spread by the Aedes mosquito, in recent years. It also had to face an outbreak of dengue fever in Key West in 2009, when the virus began circulating among local mosquitoes after a long absence. Between 2009 and 2010, there were 88 cases of dengue in the Keys, according to the Florida Department of Health.

Map of Florida showing counties with reported locally transmitted dengue cases, 2009–2013.
Virology Reports

Like Zika, dengue and chikungunya are rarely fatal, but there is also no vaccine to stop their spread.

"We can't guarantee Zika to behave as those two other viruses behave," Frieden said at a National Press Club event May 26. But they do help the CDC take a good guess for how Zika will play out in the coming months. And the prognosis isn’t severe.

The CDC advises pregnant women who traveled to the one-square-mile area in Miami after June 15 to be tested for Zika, and women who have become pregnant who frequently travel to this area to be tested in their first and second trimesters. They also recommend men and women who have traveled to this area since June 15 use condoms to prevent the spread of the virus through sex, and that women and men who have traveled to this area wait at least eight weeks before trying to conceive.

Why Florida?

Florida is more likely to be hit by the Zika virus for a few reasons (which also apply Texas, a state the CDC has warned could also be hit by Zika):

  • It has a warm, tropical climate where mosquitoes can breed year-round.
  • It's also already home to the two mosquito species known to transmit Zika: Aedes aegypti and Aedes albopictus. (The bigger concern is the Aedes aegypti variety, which has a particular fondness for biting humans.)
  • Many travelers to and from Latin America pass through Florida every day.
  • And we know the Aedes aegypti mosquitoes there have, in recent years, infected people with viruses thought to be inactive in the United States.

Zika is in Florida, but you should still remain calm

Even if the virus establishes a small foothold here, we’re unlikely to see an epidemic anything close to what Brazil and other countries in Latin America have experienced.

"Better housing construction, regular use of air conditioning, use of window screens and door screens and state and local mosquito control efforts helped to eliminate [mosquito-borne infections like malaria] from the mainland," said Lyle Petersen, director of the CDC's division of vector-borne diseases, in a statement this year.

Vox’s Julia Belluz has highlighted other key reasons not to fear Zika in the US.

  • Eighty percent of people with Zika show no symptoms.
  • Only 1 percent of pregnant women will show birth complications.
  • Condoms are effective against transmitting the disease sexually.
  • Bug repellent, bed nets, screened in windows, and removing trash and standing water around a house can all help in preventing Zika’s spread.