Dengue Fever in Travelers to the Tropics, 1998 and 1999
Dengue fever (DF) has become common in western travelers to the tropics. To improve the basis for travel advice, risk factors and dengue manifestations were assessed in 107 Swedish patients for whom DF was diagnosed after return from travel in 1998 and 1999. Patient data were compared with data on a sample of all Swedish travelers to dengue-endemic countries in the same years. Only three of the patients had received pretravel advice concerning DF from their physicians. Hemorrhagic manifestations were common (21 of 74 patients) but caused no deaths. Risk factors for a DF diagnosis were travel to the Malay Peninsula (odds ratio [OR] 4.95; confidence interval [CI] 2.92 to 8.46), age 15-29 years (OR 3.03; CI 1.87 to 4.92), and travel duration >25 days (OR 8.75; CI 4.79 to 16.06). Pretravel advice should be given to all travelers to DF-endemic areas, but young persons traveling to southern and Southeast Asia for >3 weeks (who constituted 31% of the patients in our study) may be more likely to benefit by adhering to it.

Dengue fever (DF) is an acute, self-limiting febrile viral disease of 2-7 days' duration, characterized by a sudden onset of fever and a variety of other symptoms such as severe headache, joint and muscular pain, retroorbital pain, and rash. Occasionally, hemorrhagic manifestations, such as skin hemorrhages, gum bleeding, epistaxis, menorrhagia, and gastrointestinal hemorrhage, occur. Dengue hemorrhagic fever (DHF) is a more severe disease with fever, hemorrhagic phenomena, thrombocytopenia, and plasma leakage caused by increased vascular permeability. In patients with DHF, a sometimes-fatal circulatory failure with hypovolemic shock, called dengue shock syndrome, can develop.

The dengue virus (formal name: Dengue virus [DENV]) belongs to the family Flaviviridae, which also includes yellow fever virus and Japanese encephalitis virus. Dengue virus has four serotypes, DENV-1 to DENV-4. Infection with one of these serotypes conveys life-long immunity but not cross-protective immunity to the other serotypes. Serologic analysis is difficult because of cross-reactivity between the viruses. However, together with clinical symptoms and travel history, dengue serology can yield a diagnosis. Humans are infected with dengue virus by the bite of infective Aedes mosquitoes. The most important vector is Aedes aegypti, which prefers to feed on humans during daylight hours. The incubation time is 3-14 days, most often 4-7 days.

DF is endemic in most countries in the tropical areas of southern and Southeast Asia, the Western Pacific regions, Central and South America, the Caribbean, and Africa. Transmission of DF increases during the rainy season.

With an increased travel to tropical countries, and an increased incidence of DF in these countries, DF has become the most common imported arbovirus disease in Sweden. In the absence of an effective vaccine, pretravel advice, mainly on protection against mosquito bites, is important to prevent the disease Such advice should be focused on individual risk assessments, based on available epidemiologic data. The aim of this study was, in the light of changing travel patterns, to give an update on risk factors for DF in order to form the basis for pretravel advice.