Dengue fever appears in the Florida Keys

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More than one-third of the world’s population lives in an area at risk for transmission of dengue fever, but the Florida Keys haven’t traditionally been among them.

Federal health officials report, however, that 28 residents and visitors to Key West, Fla., were infected with dengue fever between July 2009 and April 2010 — the first outbreak of the mosquito-borne disease in the continental U.S. outside the Texas-Mexico border since 1945, and the first locally acquired cases in Florida since 1934.

It’s not clear why dengue has reemerged in Florida at this time, but, according to a Centers for Disease Control and Prevention (CDC) report released on Monday, it’s a ripe breeding ground for the disease: South Florida is a popular travel destination, so there’s plenty of opportunity for travelers from endemic areas, such as Puerto Rico, to introduce the virus; mosquitoes in the area are capable of transmitting it; and the human population is largely not immune to the disease.

Over the last several decades, reported cases of dengue have more than quadrupled in Central and South America, Mexico and the Caribbean — from about 1 million in 1980-1989 to nearly 4.8 million in 2000-2007 — largely due to urbanization, increased international travel and lack of appropriate mosquito-control measures. Cases of dengue among U.S. travelers returning from these areas have also increased over the past 20 years; the disease is now the leading cause of febrile illness in people who have traveled in these regions.

The current U.S. outbreak was first discovered in August 2009, when a 34-year-old woman from Rochester, N.Y., went to her doctor complaining of typical dengue symptoms: fever, headache, malaise, chills and bloody urine. The woman had just returned from a one-week trip to Key West, where she had been bitten repeatedly by mosquitoes, and an incisive infectious-disease specialist put the two together, diagnosing her with dengue fever.

In September, a married couple in Key West who had not recently traveled outside of Florida were similarly diagnosed. The latest reported case was in April 2010 — another Key West man, age 41, who had not traveled outside the U.S. in 18 months.

In response to the initial cases, local Florida authorities in late 2009 began identifying mosquito breeding grounds, spraying the area with insecticide and launched a public education and health campaign. The CDC also surveyed the Key West community, doing blood tests on randomly selected households in search of additional cases: out of 240 people tested, 13 (5.4%) had evidence of recent dengue infections. Meanwhile Florida health officials analyzed emergency room records and blood samples taken by local doctors from patients who had had symptoms consistent with dengue, turning up an additional 24 cases.

Dengue fever is rarely fatal, but it can become severe. The most common mosquito-borne virus in the world, it causes an estimated 50 to 100 million infections and 25,000 deaths each year. There is no vaccine available yet against dengue, and no specific medications to treat an infection — though acetaminophen, rest and lots of fluids are often prescribed — so prevention (i.e., avoiding mosquito bites) is key in endemic areas. Click here for more information on dengue, including symptoms and treatment, from the CDC.

The CDC advises physicians to consider dengue fever when diagnosing patients with relevant symptoms. Indeed, many tropical diseases and infections that are typically associated with the developing world often go unrecognized by U.S. doctors, even though several million Americans, mostly immigrants and the poor, may have these conditions, according to an NPR report.