Florida Dengue Outbreak Becomes Largest in Continental US in Decades as Tampa Area Cases Top 250 This Year

TAMPA, Fla. — Florida is dealing with what appears to be the largest dengue outbreak in the continental United States in decades. State health officials have reported more than 250 locally acquired cases of the mosquito-borne illness so far this year, most of them in the Tampa area.

Most of the cases have been in Hillsborough County, which includes Tampa. Local emergencies have been declared in Hillsborough and nearby counties, and mosquito control crews are spraying around the clock to reduce the insects that carry the virus.

Federal health officials say their records on dengue outbreaks are incomplete. But data from state health departments and medical literature indicate that Florida's total is the highest for any state in a single calendar year since at least the 1940s, according to The Associated Press.

Surpassing previous records

Florida's worst year before this one was 2023, when the state recorded just under 200 locally transmitted cases.

The Tampa-area outbreak, first detected in July, is also close to surpassing the largest U.S. state outbreak in recent memory. That outbreak was in Hawaii, where 264 locally acquired cases were reported over six months in 2015 and 2016.

One person has died from dengue in Florida this year, an elderly woman from Tampa who died Sept. 4.

Puerto Rico, a U.S. territory, regularly sees far more dengue cases than any state. Nationwide, nearly 1,900 locally acquired cases have been reported this year, most of them in Puerto Rico, according to the Centers for Disease Control and Prevention.

Globally, the World Health Organization has recorded more than 2.2 million infections and nearly 1,200 deaths so far this year.

What is dengue?

Dengue is a viral infection spread mainly by Aedes aegypti mosquitoes.

Many people who are infected have no symptoms. Others develop fever and flu-like symptoms, often with severe muscle and joint pain, which led to the disease's nickname, "breakbone fever." In severe cases, dengue can cause internal bleeding, shock and death.

There are four types of dengue virus. Infection with one type gives lifelong protection against that type, but a later infection with a different type can lead to more severe illness. The antibodies from the first infection may help the new virus enter cells rather than fight it, which has made developing an effective vaccine difficult.

Most people in the Tampa area have no previous immunity to dengue, according to Dawn Wesson, an expert on mosquito-borne diseases at Tulane University.

Why Tampa?

Florida typically records more locally transmitted dengue cases than any other part of the continental U.S. Experts say this is partly because the state receives many travelers from Puerto Rico and other regions where dengue is common. When an infected traveler is bitten by a local mosquito, the virus can begin spreading in the community.

Most of Florida's cases usually occur in the Miami area, making this year's concentration around Tampa unusual. Wesson said it is difficult to know exactly why the outbreak took hold there, but travel patterns may be one factor.

As of last week, locally acquired cases in Florida had slightly outnumbered travel-related cases, 252 to 245, according to state data.

The mosquitoes that carry dengue thrive in warm, humid conditions. Experts say climate change has helped expand their range across the southern United States.

Dengue cases acquired within the continental U.S. were rare for decades. In 2009 and 2010, Key West reported the first locally acquired cases outside the Texas-Mexico border region since 1945.

Limited CDC role

The CDC would usually play a highly visible role in an outbreak of this size, but its presence has been limited this time, Wesson noted.

The agency must be invited by state officials to send disease investigators, and Florida has not made that request, CDC spokesman Jason McDonald said. The CDC has provided $800,000 in assistance to Florida's health department, he said.

How to protect yourself

Health officials and experts recommend several steps for people in areas with dengue activity:

• Use insect repellent. Apply EPA-registered repellents containing ingredients such as DEET. The mosquitoes that spread dengue bite during the day as well as at night.
• Cover up. Wear loose-fitting, long-sleeved shirts and long pants.
• Stay indoors when possible. Use window and door screens and air conditioning.
• Be careful at dawn and dusk. Mosquitoes are often most active just after sunrise and around sunset.
• Remove standing water. Empty containers, tires, flowerpots and other items where water collects and mosquitoes can breed.

Anyone who develops a high fever, severe headache, pain behind the eyes, joint or muscle pain, or a rash after possible exposure should seek medical care. Warning signs of severe dengue include severe abdominal pain, persistent vomiting, bleeding from the gums or nose, and extreme fatigue, which require emergency treatment.

A 'new normal'?

Experts warn that outbreaks like the one in Tampa could become more common as warmer temperatures and established mosquito populations make conditions favorable for the virus to spread.

"There's a good chance that this is the new normal," Wesson said.

Mosquito control efforts will continue in the Tampa area, where crews are spraying and inspecting properties for standing water. Health officials will be watching whether case numbers decline as temperatures cool later in the fall, which typically reduces mosquito activity.