Three counties around Tampa Bay are under states of emergency over a virus that, until this summer, almost nobody there caught at home. Florida has recorded 252 cases of locally acquired dengue since July, more than in any year since the state’s modern surveillance began. Hillsborough County, home to Tampa, accounts for 223 of them. Before this year it had recorded two local cases in a decade .

The count was still rising at last report, with 62 new cases in the final full week of September. An 80-year-old Tampa woman bitten near her home on Bayshore Boulevard died on September 4 . On Monday, Broward County confirmed its first local case of the year, the eighth Florida county with local transmission in 2026.

“Locally acquired” is the phrase that matters. Most dengue diagnosed in the United States is caught abroad and carried home. In 2024, a record year for US dengue, 97% of cases were travel-associated and only 105 were acquired locally, across three states. A local case means a Florida mosquito bit an infected person in Florida and passed the virus to someone else. Florida has now logged more than twice the country’s entire 2024 local total, most of it in one county.

Pasco County declared a local emergency on September 23. Hillsborough and Pinellas followed the next day, and all three have extended their orders to October 8. The declarations rest on Chapter 252 of the Florida Statutes , the same emergency-management law counties invoke before a hurricane.

What the orders unlock shows what slows mosquito control in ordinary times. Pinellas’s resolution suspends the usual rules for contracts, purchasing and hiring. It authorizes crews “to enter upon lands during daylight hours, whether public or private,” and to remove “without notice, stagnant water or other breeding places for mosquitoes.” Hillsborough’s order, signed by County Administrator Bonnie Wise, also provides “a path for federal reimbursement of certain expenses,” even as President Donald Trump has declared war on Washington, D.C.’s mosquitoes , ordering a 90% cut by 2028 in the capital’s invasive mosquitoes, including the same species now spreading dengue in Tampa.

The right of entry is the provision to watch. Aedes aegypti , the mosquito behind this outbreak, breeds in flowerpot saucers, buckets, tires and bottle caps, almost always within a few yards of a house. The decisive habitat is private property. In normal times a crew that finds a neglected backyard full of standing water has to knock, wait and come back. During a dengue outbreak, that backyard stops being a public nuisance and becomes a public hazard.

Hillsborough’s mosquito program had never faced dengue on this scale. For assistance, the county signed mutual-aid agreements with Manatee and Pasco counties for helicopters and pilots, and cross-trained Public Works employees to canvass neighborhoods and run nighttime truck spraying. Lee County’s mosquito district flew in four helicopters , which spray larvicide by day and adulticide by night. Insecticide alone has cost the county about $250,000 so far.

Spraying from the air is a blunt tool against this particular mosquito. Ae. aegypti bites during the day and rests indoors and in sheltered corners, where spray from a helicopter or a truck has little reach. Miami-Dade and Lee counties have spent the decade since Zika building programs aimed specifically at it, including releases of male mosquitoes infected with Wolbachia , a bacterium that causes their matings with wild females to produce eggs that never hatch. Miami-Dade receives more than ten times as many travelers with dengue as Hillsborough does, and so far it has eight local cases this year.

More infected travelers would be the obvious explanation, but the total barely moved. Through late September, Florida had 245 travel-associated cases, up about 11% from 220 at the same point in 2025 . Hillsborough’s went from 11 to 13. Tampa’s summer, per the National Weather Service , was less than a degree above normal and drier than usual.

What changed was where imported infections came from and which serotype they carried. Of this year’s 245 travel-associated cases, 201 were in people infected during recent travel to Cuba , up from 140 a year earlier. Last year most such infections were DENV-4, one of dengue’s four serotypes. This year most are DENV-2, as Cuba’s epidemic runs far above normal and fuel shortages curtail fumigation on the island. Imported DENV-2 cases rose roughly eightfold, from 22 to 183. Of the 232 local Florida cases that have been typed, 230 are DENV-2.

Tampa’s outbreak began with a virus carried in from Cuba, where fuel shortages are curtailing mosquito control. To a mosquito-borne virus, the two places form one transmission system, joined by daily flights. Each infection prevented in the Caribbean is one fewer spark landing in Florida, which gives the United States a direct stake in controlling dengue beyond its own borders.

The best evidence on how Florida’s outbreaks start comes from a preprint posted in May by Nathan Grubaugh’s group at the Yale School of Public Health and the Florida Department of Health. They sequenced dengue from 133 local and 294 travel cases between 2010 and 2024. Florida’s outbreaks, they found, were caused by “frequent short-lived DENV introductions, primarily from the Caribbean,” and they found no evidence that any lineage survived from one season to the next. The paper has not yet been peer reviewed.

Tampa will test that history. A single serotype across nearly every typed case sounds more like one introduction that ran away, although it also fits several separate introductions of the same serotype. Dengue expert and Northeastern University Professor Michael Johansson has said it is unclear whether the outbreak is one sustained chain or “multiple smaller introductions.” One chain would mean Tampa kept the virus’s reproduction number above one for months.

Largest in the Continental US?

The Associated Press calls it the largest outbreak in the continental United States in decades. Hawaii’s Big Island had 264 local cases between September 2015 and March 2016, a dozen more than Florida’s current count. Florida’s next weekly report will probably pass it.

Hawaii’s outbreak lasted six months. Florida’s has run about three so far. The Asian tiger mosquito , which spreads its bites among animals as well as people, was the main culprit during the Hawaii outbreak. Tampa’s is fueled by Ae. aegypti , which feeds almost exclusively on humans, in a metro area of three million people.

None of this approaches Puerto Rico, the US territory where dengue is endemic and case counts run much higher than in any of the 50 states .

Florida is not the only state seeing local spread. Virginia confirmed its first locally acquired dengue case in August. Following publication of an outbreak investigation of a cluster of dengue cases in Los Angeles, I argued that rising introductions will continue to push marginal places over the transmission threshold. Tampa appears to have crossed that boundary this year by a substantial margin.

The emergency orders expire Thursday unless renewed. Cooler nights in November will probably do more to end this outbreak than spraying from helicopters. The Yale team’s genomes, covering 2010 through 2024, show no lineage surviving the winter. The last documented case of that was in Key West in 2009 and 2010 . If Tampa’s DENV-2 comes back next summer before any new strain is introduced, it will be the first since.