Florida’s dengue outbreak highlights the importance of recognizing symptoms, identifying warning signs, and preventing mosquito bites. Ubong Johnson, MD, explains local transmission, diagnostic testing, treatment, and practical prevention measures.
Florida has recorded a recent spike in the number of dengue fever cases, with one death confirmed in September. The latest weekly update posted by the Florida Department of Health (Week 39, September 27 to October 3) confirms 296 locally acquired cases across 8 counties.1
Hillsborough County takes the biggest hit, with 259 cases and one confirmed death: an 80-year-old Tampa woman who died in September. Other affected counties are Pinellas (20), Miami-Dade (8), Orange (3), Pasco (3), Palm Beach (1), Polk (1), and Broward (1).1
The Florida dengue spike is likely due to international travel, an increase in local mosquito population, and low population immunity. These are plausible contributing factors; however, the surveillance report does not show that any one of them caused this outbreak. As an international travel hub, trade route, and center for tourism, Florida sees a continuous influx of visitors from endemic areas across Latin America and the Caribbean, some of whom are infected with the dengue virus.2
When Aedes aegypti, a mosquito species that prefers to feed in the daytime, or, less frequently, Aedes albopictus, bites a person with the dengue virus circulating in the blood, it can pick up the virus. This person may be an international visitor, a Florida resident returning from travel, or someone already infected locally, and may have no symptoms. When an infected mosquito bites someone else, it can spread the virus. There are 4 serotypes of dengue virus: DENV-1, DENV-2, DENV-3, and DENV-4. Of the local cases serotyped in the Week 39 report, 273 were DENV-2, and 2 were DENV-3.
Because Aedes aegypti is a nervous mosquito that is easily disturbed while feeding, it will usually bite more than one person before completing a blood meal.3 More bites create more opportunities for transmission. As transmission bites and transmission continue, the dengue virus eventually enters the local population and starts to spread amongst locals without the need for international hosts.4
Heat contributes to the increasing rate of dengue fever transmission by increasing the local mosquito population and by shortening the extrinsic incubation period. The virus typically replicates in a mosquito’s midgut and spreads to other tissues, including the salivary gland, before transmission is possible. WHO says this takes about 8 to 12 days at 25–28°C. In hotter seasons, the virus can mature more quickly, leading to faster transmission.5
Since prior infection generally gives long-lasting protection against the same dengue virus serotype and only temporary protection against the other serotypes, people living in endemic areas usually develop a type of immunity against dengue fever called homotypic immunity.6 A second infection with a different dengue virus serotype can result in a more severe disease, as previously acquired antibodies act as “Trojan horses” that permit easier entry of the virus into the cell.
Symptoms of dengue fever, if they appear, usually begin 4 to 6 days after the infecting bite. CDC’s yellow book describes a typical incubation of 5 to 7 days, within a range of about 3 to 10 days.7 Some people experience no symptoms.
Where symptoms are present, dengue fever has 3 courses: a febrile phase, a critical phase, and a recovery phase.8
The febrile phase lasts 2 to 7 days and can occur in 2 phases. It begins with a high fever that reaches up to 104°F (40°C), a headache, and pain around the eyes. There may be muscle soreness, joint pain, fatigue, facial flushing, and loss of appetite.9 A rash usually shows up around 2 to 6 days after the fever starts, and there may be some bleeding trouble. In children and in patients who later develop a severe form of the disease, there may be signs of stomach trouble, such as nausea and vomiting.
Most patients recover at the end of the febrile phase. The critical phase typically begins when the fever subsides and lasts 24 hours. About 1 in 20 people who become ill with dengue develop severe dengue.8 In severe dengue, fluid seeps out of blood vessels. This can cause fluid build-up around the lungs and in the abdomen, presenting as difficulty in breathing or abdominal swelling, respectively.
Severe dengue is characterized by plasma leakage that causes shock or respiratory distress, severe bleeding, or severe organ involvement. Early compensated shock can occur before hypotension. A marked reduction in blood sodium can also occur, although this doesn’t define severe dengue. Some patients may experience bleeding due to a drop in platelet count, which shows up as blood in stool, blood in vomit, and excessive menstrual bleeding.10
As fluid leakage from blood vessels subsides, patients in the critical phase enter the recovery phase and begin to improve.
Clinicians suspect dengue when a person has an acute fever and 2 or more classic symptoms, such as pain behind the eye, severe muscle ache, nausea/vomiting, or a maculopapular rash, especially if this person lives in or has recently traveled to an area with dengue transmission. Dengue fever is not confirmed clinically. Some lab work is needed to distinguish the disease from other conditions that resemble it, such as COVID-19, acute gastroenteritis, or leptospirosis. Testing helps confirm the diagnosis, but management of suspected dengue should begin without waiting for results.
Reverse Transcription-Polymerase Chain Reaction (RT-PCR) detects dengue virus in serum and can identify the infecting serotype. Sensitivity depends on the assay, the specimen, and the timing. CDC recommends a nucleic acid test, such as RT-PCR, plus IgM or NS1 antigen plus IgM, during days 0 to 7 of illness. After day 7, IgM is the primary test. A negative RT-PCR or NS1 doesn’t rule out dengue.11
Dengue fever can be treated at home or in the hospital. At home, patients can benefit from drinking enough fluids, getting adequate rest, and taking acetaminophen for fever or pain. Aspirin and other NSAIDs, including ibuprofen, should be avoided because they can increase the risk of bleeding. Patients with warning signs, certain underlying health conditions, or an inability to keep down oral fluids may need hospital care.
In the hospital, patients may be given IV fluids with careful monitoring to avoid fluid overload. Blood transfusion is considered when there is clinically significant bleeding or suspected occult bleeding.
If you are currently experiencing any symptoms of dengue fever or know someone who is, seek medical care or encourage them to do so.
Dengue fever is preventable.12 Prevention aims to break transmission cycles by stopping the vector from multiplying and biting people, as well as directly protecting individuals from the effects of a mosquito bite, should one get bitten.
You can protect yourself from mosquito bites by using insect repellent, wearing loose-fitting long-sleeve clothes, using insecticide-treated nets, using air conditioners, and controlling mosquito populations around you.
You can eliminate potential mosquito breeding grounds by emptying, covering, or cleaning containers that hold stagnant water. Public health agencies may support this by making larvicides available for use in non-potable water systems.
Travel precautions can reduce the risk of the virus being introduced and spreading. CDC recommends that travelers returning from dengue-risk areas prevent mosquito bites for 3 weeks, even if they feel well, and watch out for symptoms for 2 weeks.
There are currently no dengue vaccines available in the United States, under CDC guidance. Dengvaxia has been discontinued and is no longer available. And Qdenga is not available or recommended in the United States. Travelers should review destination-specific notes, receive pretravel advice, and prevent mosquito bites. As vaccine research advances, dengue vaccines may soon be available in the US.13
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