Is Dengue Fever on the Rise in the U.S.?

From the WebMD Archives

Dec. 23, 1999 (Atlanta) -- Dengue fever, a viral illness most often seen in the tropics of Asia and Africa, is becoming a bigger threat here on U.S. soil. Florida researchers report in the Dec. 24 issue of the CDC's Morbidity and Mortality Weekly Report that incidence of dengue is higher than previously reported in their state. Experts call for improved prevention, surveillance, and reporting to prevent the spread of the virus to other parts of Florida and to other states.

But some states seem to be having their own problems with dengue already. In an unrelated report, the Texas state department of health has announced that a girl who died earlier this month is the first casualty of a dengue outbreak there that has infected 51 people this year -- the biggest outbreak there this decade. It's thought the girl picked up the disease during a trip to Mexico.

Dengue fever -- mainly transmitted via the Aedes aegypti mosquito -- is commonly referred to as "break-bone fever" due to pain so intense that bones are often felt to be breaking. In addition to such pain, infection with any of dengue's four types can lead to acute illness with joint pain, headache, fever, rash, and hemorrhage. After infection with one type, the antibodies that are produced usually protect the patient from future infections related to that particular serotype. However, infection with a different type puts the patient at risk for a more severe form of the illness, marked by internal bleeding, called dengue hemorrhagic fever. Patients usually recover from dengue within a few days, though related fatigue can last as long as a month or two.

"In the last 10 years, a mean of 1.3 cases per year were reported in the state [of Florida]," says lead author Julia Gill, PhD, MPH. "The number of cases reported to the state was so low that I couldn't believe that that was the true number of cases. ... I thought [by conducting this surveillance study] we'd find a lot more cases." Gill is with the Florida Department of Health in St. Petersburg.

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This laboratory-based active surveillance study was implemented in Florida for a year starting in April of 1997. Sixty-seven county health department epidemiologists were mailed information explaining the program and requesting participation; the dengue case definition, specimen requirements, and transport instructions were provided. Departments were instructed to distribute enclosed materials to clinics, hospital ERs, health departments, and infectious disease physicians. Samples were tested, and those found to be in the acute phase of the disease were sent to the CDC for further analysis.

In Florida, 83 suspected dengue cases were analyzed. Of these cases, recent dengue infection was detected in 22%. Of the cases studied, all four dengue types were identified. In 29% of the suspected cases, dengue was ruled out, and in 49% of the cases, a diagnosis was indeterminable due to inadequate blood samples.

In the confirmed cases of dengue, 56% were second infections, 11% were the person's first infection, and the remainder were indeterminable due to a lack of necessary laboratory tests. Of the confirmed cases, 39% had hemorrhagic manifestations. Also, of the confirmed cases, all had traveled from countries within 10 days of the onset of illness: six patients had traveled from Haiti, three from Puerto Rico, two from Columbia, two from Venezuela, one from Barbados, one from Nicaragua, and one from Thailand.

Usually, the viremic period -- time that the virus circulates in the blood stream -- is only four days, according to Gill. "One of the theories has been that it would be very difficult to import the disease and have local mosquitoes pick it up and start local transmission because the viremic period was so short," she says. "The theory was that, by the time people traveled back into the state, perhaps they would not be viremic anymore. But we were able to isolate virus from individuals while they were in the state of Florida, and that demonstrates that the risk of future transmission is there."

Is it possible that dengue fever will start to spread within Florida and to other states? Yes, says Gill. "The last time dengue was ... [a problem] in Florida was in the 1930s," she says. "There were big outbreaks in Tampa and Miami. There hasn't been any local transmission documented since then. [But,] certainly, individuals and mosquitoes that could be infected are coming in and out of the state regularly. The incidence of dengue in the surrounding countries is increasing dramatically."

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Gill says that the incidence of dengue fever is probably a lot higher than that detected in this study. The majority of dengue illnesses have flu-like symptoms or no symptoms at all, so probably only the sickest people sought medical care, she says.

What is the solution? Patients traveling to countries where dengue fever is present need to protect themselves from mosquito bites by wearing protective clothing and using mosquito repellent, according to Gill. They need to see a physician if they become sick after returning home. When diagnoses of dengue are confirmed, patients need to protect themselves from mosquito bites for the period that they are sick, she says. "During that four-day period when they may be viremic, they need to protect themselves from mosquitoes so the mosquitoes don't bite them, pick up the virus, and possibly transmit it to other people," she says.

Vital Information:

  • Dengue fever is a virus transmitted via mosquitoes that can cause intense "bone-breaking" pain, and though recovery takes only a few days, related fatigue can last a month or two.
  • A new report shows that the incidence of dengue fever in Florida is higher than previously suspected.
  • When traveling to countries where dengue fever is a concern, one should wear protective clothing and insect repellent.
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