Clinical Presentation
Most travelers infected abroad become ill within 12 weeks after returning to the United States. However, some diseases, such as malaria, may not cause symptoms for as long as 6-12 months or more after exposure (see Table 2-3). If travelers become ill after they return home, even many months after travel, they should be advised to tell their physician where they have traveled. In particular, fever in a traveler returned from a malarious area should be considered a medical emergency. The possibility of malaria as a cause of the fever should be evaluated urgently by appropriate laboratory tests and qualified personnel, and testing should be repeated if the initial result is negative. In this regard, primary care physicians, general medicine practitioners, pediatricians, emergency medicine physicians and every health-care worker dealing with a febrile returned traveler from a malaria- endemic area should take the steps to ensure the patient has serial blood smears evaluated and consider hospitalization if there is any need for observation.
In evaluating patients seeking medical care, it is essential to obtain a detailed history of exposures such as insect bites, swimming in freshwater, animal bites, eating raw meat, seafood, or unpasteurized dairy products, and sexual contacts. Answers to these questions may provide important clues for diagnosis of a particular illness or syndrome in returned travelers (1-4). In addition, when suspecting an infectious disease, calculating an approximate incubation period is a useful step in ruling out possible etiologies (2). For example, fever beginning 3 weeks or longer after return greatly reduces the probability of dengue, rickettsial infections, and viral hemorrhagic fevers in the differential diagnosis. This important step helps focus the differential diagnosis on probable causative agents and eliminates unlikely considerations. As indicated by exposure history, time course of illness, and associated signs and symptoms, initial investigations for febrile travelers may include prompt evaluation of peripheral blood for Plasmodium species; a complete blood cell count with differential; liver enzymes; urinalysis; culture of blood, stool, and urine; and chest radiography. More specific diagnostic assays may be useful initially for diseases such as leptospirosis (serology) and acute HIV infection (RNA viral load). However, sometimes acute- and convalescent-phase serologies are required to confirm a particular diagnosis such as many rickettsial infections (2-4).
Since most primary-care physicians have little expertise in tropical diseases, a newly returned, ill international traveler should be evaluated by an infectious disease or tropical medicine practitioner. For assistance in finding a provider who practices clinical tropical medicine, one may access the American Society of Tropical Medicine website for a listing by state at http://www.astmh.org or the International Society of Travel Medicine at http://www.istm.org.
It may be prudent for asymptomatic international travelers who have been abroad for many months or longer, particularly in developing countries, to be screened for certain diseases. The decision to screen for particular pathogens will depend on the travel and exposure history. For example, travelers who have engaged in casual unprotected sex or have received an injection, a body piercing, or a tattoo may be screened for HIV, hepatitis C and other sexually transmitted diseases, and, if not immune, hepatitis B. Sometimes, testing for hepatitis C RNA viral load or HIV RNA viral load is recommended for travelers with high-risk factors presenting with a febrile illness. In addition, performing a tuberculin skin test to identify conversion in those travelers who were previously tuberculin negative is recommended, particularly after a prolonged stay in a developing country. Travelers who have been exposed to freshwater in areas endemic for schistosomiasis should be screened for this infection by serology and stool and/or urine tests (20). Eosinophilia in a returned traveler suggests the possibility of a helminth infection, of which the most important is strongyloidiasis. If left untreated, this infection may last for the lifetime of the host, and in an immuno-compromised person it has the potential to disseminate.
