Severe dengue infections may go unrecognized in international travelers

Dengue is the most important emerging disease among international travelers, with a 30-fold increase in incidence over the past 50 years worldwide. Like malaria, dengue is transmitted to humans by mosquitoes.

Most cases are mild. Symptoms include fever, rash, headache, pain behind the eyes, and muscle and joint pain. According to the WHO, dengue hemorrhagic fever (DHF) is characterized by fever, low platelet count, clinical evidence of leaking capillaries, and spontaneous bleeding or fragile blood vessels. The most serious cases can lead to shock and death. There is no cure for dengue infection, but management of the disease's effects can prevent the worst outcomes.

The study, conducted by Ole Wichmann, MD, MCTM, DTM&H, at the Robert Koch Institute in Berlin, Germany, and colleagues throughout Europe, collected data through the European Network on Surveillance of Imported Diseases at 14 sites in 8 European countries.

Out of more than 200 patients treated for dengue infection at these sites over two years, less than 1 percent fit all four criteria necessary to meet the WHO definition of DHF. However, 11 percent had at least one manifestation of severe dengue disease, and a total of 23 percent required hospitalization due to dengue-related symptoms.

“Dengue exists more as a continuous spectrum,” Dr. Wichmann said. “Severe disease can be present in patients who do not fulfill all four DHF criteria.”

“The term 'dengue hemorrhagic fever' puts undue emphasis on bleeding,” he added, noting that plasma leakage and shock can occur without it. “Clinicians who mainly focus on bleeding…may miss the most important conditions that require hospitalization and treatment.”

Their findings also showed that travelers who acquire a second dengue infection are more at risk for severe cases of dengue, although some patients had severe symptoms when infected during their first trip to a dengue-endemic country.

It is becoming more and more crucial that health care providers understand the clinical spectrum of dengue and its diagnosis. “Given the increase in business travel and other travel, and the global spread of dengue fever, these findings have important implications for the future burden of severe imported dengue infections,” Wichmann said. “It will also be of great interest to business and leisure travelers, and expatriates, who have experienced one dengue infection and are concerned about this risk of returning to a dengue endemic area.”

As a next step to their study Wichmann highlighted the need for more inquiry into a clinical definition of dengue. “In order to perform more uniform surveillance and research, including vaccine trials, studies are urgently needed to establish new and more robust definitions for severe dengue.”