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

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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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