Dengue is in Citrus County. The cold that ends it is still weeks away
Two Citrus County dengue cases were caught here, not on a trip — making Citrus the ninth Florida county with local spread in the largest U.S. dengue outbreak in decades. Whether it grows depends on a temperature clock most people never hear about.
- Two Citrus County cases were locally acquired — caught from mosquitoes here, not while traveling. Citrus is the ninth Florida county with local dengue this year.
- Statewide: 368 locally acquired cases through Oct. 10 — Hillsborough 310, Pinellas 37, Miami-Dade 9, Orange 5, Pasco 4, and one each in Broward, Palm Beach and Polk — nearly double the 2023 record of 199, and still climbing, with 72 added in the last reported week.
- Temperature runs the outbreak twice: dengue needs about 6.5 days inside the mosquito at 86°F before she can pass it on, about 15 days at 77°F — and near 68°F the virus generally stalls. The mosquito herself stops feeding below about 58°F, but she bites in the daytime and indoors.
- Inverness averages 61°F nights in October and 53°F in November; December, at 46°F, is when the season genuinely ends here. Until then: dump standing water, mind screens and repellent, and take a fever seriously.
The Florida Department of Health in Citrus County issued a mosquito-borne illness alert on Monday, Oct. 19, after two cases of dengue were confirmed as locally acquired — meaning the people infected caught the virus from mosquitoes here in Citrus County, not while traveling. Dengue is not contagious from person to person. It moves when an Aedes aegypti mosquito bites an infected person, carries the virus for a while, and then bites someone else.
Citrus is the ninth Florida county to confirm local spread this year. In the state health department's most recent weekly arbovirus report, covering Oct. 4–10, Florida had logged 368 locally acquired dengue cases: 310 in Hillsborough County, 37 in Pinellas, nine in Miami-Dade, five in Orange, four in Pasco, and one each in Broward, Palm Beach and Polk. The two Citrus cases were confirmed after that report closed, so they will appear in the next one.
The outbreak is not winding down on its own yet. The state added 72 new local cases in the week ending Oct. 10, after adding 44 the week before and 62 the week before that, and more infections began in September than in any other month this year. One Hillsborough County death has been confirmed. Hillsborough, Pasco and Pinellas counties have declared local states of emergency to speed up mosquito control, and 17 counties sit under state mosquito-borne illness advisories or alerts.
For scale: Florida recorded 62 locally acquired cases in all of 2025, 68 in 2022 and 199 in 2023 — the previous record year, when the outbreak centered on Miami-Dade. This year's outbreak is centered on Tampa Bay instead, and at 368 cases and counting it is the largest dengue outbreak in the United States in decades. Nearly all of it — 341 of the 368 cases — is a single virus type, DENV-2, and 20 mosquito pools have tested positive for the virus, 19 of them in Hillsborough.
The mosquito at the center of it, Aedes aegypti, is not a swamp mosquito. It is a house mosquito. It breeds in containers around homes — buckets, old tires, plant saucers, pool covers, anything that holds a little water — lives its life close to where it hatched, bites during the daytime, and will follow people indoors. That behavior is why health officials keep repeating the same unglamorous advice: dump standing water, fix torn screens, cover up, and use EPA-registered repellent.
What decides how long this lasts is temperature, and it works on the outbreak twice. First, the virus: after a mosquito picks dengue up, it has to incubate inside her before she can pass it on. Researchers put that wait at about six and a half days at 86°F, and about 15 days at 77°F. Near 68°F, in laboratory studies, the virus generally failed to reach the mosquito's salivary glands at all — she dies of old age before she can spread it. Cooling weather stretches that clock until the chain breaks.
Second, the mosquito herself. Below roughly 58°F she grows sluggish and stops feeding; below about 50°F she can barely move. But her young cheat the calendar — in cool water, her larvae can hold in that stage for months and resume when it warms back up. And because she bites in the daytime, a cold night followed by a warm afternoon still leaves her a working day.
Read against the Nature Coast's own calendar, that is why this is not over yet. Inverness averages highs of 84°F and lows of 61°F in October — still squarely inside the mosquito's comfort zone, and October cases are the predictable result. November averages 78°F and 53°F: nights fall below the feeding line, afternoons do not, and the virus clock runs so slowly that transmission fades through the month rather than stopping on a date. December averages 72°F and 46°F, and that is when the season genuinely ends here. Hurricane Isaias stretched the wait: the storm left standing water across the county right at the start of the cool-down, and every container still holding it is a nursery.
Until the cold finishes the job, the practical part: about one in four people infected with dengue get sick, usually within two weeks of the bite — fever, severe muscle and joint pain (dengue's old name is breakbone fever), pain behind the eyes, sometimes a rash. Federal health guidance advises acetaminophen for the fever and pain, and avoiding aspirin and ibuprofen, which can raise the risk of bleeding. About one in 20 people who get sick develop severe dengue, and its warning signs tend to appear a day or two after the fever breaks: stomach pain, repeated vomiting, bleeding from the nose or gums, blood in vomit or stool, extreme tiredness. Those mean an emergency room, not a wait-and-see.
DOH-Citrus says it is working with Citrus County Mosquito Control to step up truck fogging, aerial larviciding and ground inspections for breeding sites. The state's next weekly report will show whether Citrus stays at two cases — and whether Florida's October curve finally bends the way the thermometer says it should.