CDC Activates Level 3 Emergency Response as Florida Dengue Cases Hit 425 Locally Acquired

The CDC has activated a Level 3 emergency response for dengue in Florida. It is the agency's eighth emergency activation this year.

By CDC figures, Florida has recorded 745 dengue cases in 2026. Of those, 425 were locally acquired, meaning the patient caught the virus from a Florida mosquito rather than on a trip abroad. Most are in the Tampa area.

That makes this the largest dengue outbreak in decades in any U.S. state. Federal health officials say outbreak data are limited, but state health reports and medical journals point to the most cases in any state in a calendar year since at least the 1940s. Florida's previous worst year was 2023, with just under 200 local cases.

How the outbreak grew

Hillsborough County's health department announced the first confirmed local case on July 28 and started county mosquito control.

By Sept. 24, with 143 confirmed cases across Hillsborough, Pinellas and Pasco, Hillsborough County Administrator Bonnie Wise declared a local state of emergency. Pinellas commissioners declared their own the same day. Wise said the declaration lets emergency managers act quickly and "provides a path for federal reimbursement of certain expenses."

The Tampa Bay Times reported that Florida's first dengue-related death this year was an 80-year-old Hillsborough County woman who died Sept. 4.

The state tally then climbed fast. It stood at 252 local cases through Sept. 26 and 368 through Oct. 10, a jump of 72 in the latest weekly report alone. The state's Week 40 report, covering Oct. 4 to Oct. 10, put 310 of those in Hillsborough and 37 in Pinellas. It counted 288 more cases linked to travel and listed eight counties with local transmission. Seventeen counties were under a state mosquito-borne illness advisory or alert as of Oct. 10.

Hillsborough mosquito teams have been using aerial spraying. Pinellas crews are going door-to-door near treatment areas, offering to help residents find breeding sites and treat them with the resident's approval.

What the CDC is seeing

On a clinician call, CDC experts said the local cases are primarily DENV-2, one of four dengue serotypes. Men account for 54% of cases, the median age is 43, and 45% of patients are between 30 and 49.

About 47% of cases required hospitalization. The CDC said that rate may point to under-reporting of milder infections.

Chris Braden, acting director of the CDC's National Center for Emerging and Zoonotic Infectious Diseases, laid out the concern in an email to staff: "Given the widespread presence of Aedes aegypti mosquitoes and with recent hurricane-related rainfall, continued domestic transmission remains a concern."

The same activation covers the Republic of the Marshall Islands, which has declared a state of emergency on Ebeye and Majuro. Braden said the CDC has provided programmatic support and deployed an Epi-Aid team there. The year's other activations include Cyclospora, Ebola, measles, hantavirus, New World screwworm, the World Cup safety effort and the Potomac River wastewater spill near Washington.

Why it is happening in Florida now

Adam Waickman, a dengue researcher at SUNY Upstate Medical University, said the continental U.S. historically avoided dengue because it lacked mosquitoes able to carry the virus. "The reason we're seeing this sustained transmission now is that the species of mosquito that are capable of transmitting the infection are now much more prevalent in Florida," he told MedPage Today.

Aedes aegypti is the more competent vector, Waickman said. Aedes albopictus can also transmit dengue. Its range reaches into Pennsylvania, and Aedes aegypti's has extended as far north as Virginia.

Waickman also said 70% to 90% of dengue infections are asymptomatic, so "the numbers we're seeing in Florida are just the tip of the iceberg in terms of who's actually being infected."

The disease is not contagious person to person. The Florida Department of Health says it spreads through the bite of an infected mosquito. Symptoms include fever, severe muscle and joint pain, and sometimes a rash. No widely available medicine treats it, according to the World Health Organization. Prevention comes down to mosquitoes. Pasco's health department tells residents to drain standing water around homes and businesses at least once a week, wear long sleeves and pants, and use repellent.

Spreading beyond Tampa Bay

The Florida Department of Health in Citrus County said Oct. 19 that it had confirmed two locally acquired cases. The county has stepped up truck fogging, aerial larviciding and ground inspections. The department has not said where the patients live, when they fell ill, whether either was hospitalized, or whether one is the case the county announced in August. Citrus did not appear in the state's Oct. 10 local-case list. County notices often run ahead of the weekly state report.

Citrus is one of Florida's oldest counties. About 36% of residents are 65 or older, according to Census figures cited by the Citrus County Chronicle.

On Oct. 21, the health department in Seminole County, near Orlando, confirmed a locally acquired case and issued the county's first mosquito-borne illness advisory of 2026, WFTV reported.

It remains unclear whether the Citrus and Seminole cases are part of the Tampa Bay chain or separate introductions. No serotype has been released for the Citrus cases, and the state's next weekly arbovirus report will show whether either county enters the official count.