Florida health officials have counted 252 locally acquired dengue cases so far this year, with most in Hillsborough County, home to Tampa. The outbreak appears to be the largest in the continental United States in several decades. Local authorities have declared emergencies; workers spray for mosquitoes and check properties for standing water.
The outbreak and its toll
As of last week, Florida had recorded 252 locally acquired cases, more than the 245 cases linked to travel. At least 13 Hillsborough County cases involved travelers, according to the state. The outbreak came to light in July and centers just north of Tampa.
The current total is approaching the record set during a six-month dengue outbreak in Hawaii in 2015-2016, when officials reported 264 locally acquired cases. Federal health officials said available information from state health departments and medical journals suggests Florida has reported more dengue cases in a calendar year than any state since at least the 1940s. They cautioned that their outbreak data is limited.
Florida’s previous worst year was 2023, when officials reported just under 200 locally spread cases. Florida usually has the most locally transmitted cases in the continental United States. Puerto Rico is consistently hit harder, with totals far higher than those recorded in any of the 50 states. The Centers for Disease Control and Prevention reported nearly 1,900 locally acquired U.S. cases this year, most in Puerto Rico.
One Floridian has died of dengue this year: an elderly Tampa woman who died Sept. 4. Mosquitoes spread the virus that causes dengue. Many infected people don't get sick; others develop fever, flu-like symptoms and aches. The disease is nicknamed “breakbone fever” because some patients suffer excruciating pain. Severe cases can cause bleeding, shock and death.
Local response and outside assistance
Tampa-area workers spray day and night to reduce mosquitoes that transmit disease. They're also checking properties for pooled water, including water in tires where mosquitoes might breed. Officials in Hillsborough and nearby counties have declared local emergencies.
Dawn Wesson, a Tulane University expert on dengue and other mosquito-spread diseases, said Florida tends to see many cases partly because travelers arrive from Puerto Rico and other places where dengue circulates. Cases usually cluster in southern Florida, around Miami. Wesson said it was hard to say what was driving this year’s surge near Tampa, though travel patterns may be partly responsible.
Wesson said the CDC would traditionally be highly visible in a situation like this, but it hasn't been this time. CDC spokesman Jason McDonald said state officials must invite the agency in, and Florida hadn't asked CDC disease investigators to come. McDonald said the agency provided $800,000 in assistance to the state health department.
Mosquitoes, climate and prevention
Dengue-carrying mosquitoes live in Florida and some other hotter U.S. locations. Experts say climate change has helped the insects expand their geographic reach. For decades, most dengue infections in the continental United States involved people infected while traveling internationally, alongside locally acquired cases in Puerto Rico. In 2009-2010, Key West recorded the first dengue cases acquired in the continental United States outside the Texas-Mexico border since 1945.
Worldwide, more than 2.2 million infections and nearly 1,200 deaths have been reported this year, according to the World Health Organization. Wesson said most people in the Tampa area don't have prior immunity to any form of dengue. The virus has four types. A first infection builds lifelong antibodies against that type, but antibodies from an earlier infection may fail to neutralize another type and may help it enter immune cells and replicate, making an effective vaccine difficult to develop.
Experts recommend EPA-registered insect repellents containing ingredients such as DEET, loose-fitting long sleeves and long pants, and staying indoors behind screens or in air-conditioned rooms. Mosquitoes can bite at any time of day, though activity tends to peak just after sunrise and around sunset. People should remove pooled water from their properties. Wesson said climate conditions and persistent mosquito populations will likely make local dengue outbreaks more frequent: “There's a good chance that this is the new normal,” she said.