Tampa outbreak pushes Florida's locally caught dengue past its imported cases

The year's turn to a local majority is narrow. Locally caught cases lead imported ones by seven ^[18]. Waddell told Live Science the travel count is not unusually high ^[4], so nearly all of the change sits in the local column. Until the past few years, most dengue cases reported in Florida were caught abroad ^[6].

Waddell's fivefold figure compares this year with the previous four at the same point on the calendar ^[5]. The choice of window matters. Miami's 2019 outbreak, which Live Science put at over 200 cases ^[14], falls outside it. If those cases were mostly local, that year was in the same range as this one ^[2]. The 2022 to 2024 Miami outbreaks fall inside the window ^[14]. A local count five times any of those years is hard to reconcile with outbreak totals in the hundreds. Both can hold only if the Miami totals include imported cases, or if most of their cases came later in the year than this point. Live Science does not say which.

Reported cases are a partial count in any year. Only about one in four people exposed to the virus develop symptoms ^[8], so the local tally is a floor on local infections. Dengue does not pass from person to person; Aedes aegypti and Aedes albopictus mosquitoes carry it to the people they bite ^[7]. Each locally caught case means a mosquito in Florida was infected ^[7].

The broader rise has a probable cause. Global dengue cases grew tenfold between 2000 and 2019 ^[10]. Live Science reports that climate change is the likely driver: higher temperatures widen the range of Aedes aegypti, and warmer conditions speed up both the mosquito's life cycle and the virus's replication ^[11]. U.S. cases reached nearly 3,800 in 2024, more than 300% above the previous decade's annual average ^[12]. The thing this doesn't tell you is why Hillsborough carries this year's outbreak. University of Florida disease ecologist Panpim Thongsripong told Live Science the region normally sees just a few sporadic cases ^[15].

I think planning for local spread as the default is justified for south Florida. Outbreaks recur there every year ^[13], and outbreak totals, whatever their mix of local and imported cases, have climbed from about 50 or fewer to several hundred ^[14]. For Tampa, the record so far is one season ^[16]. Several counties have responded by declaring a state of emergency ^[1].