Carlos Franco-Paredes

Risk of Illness in Travelers

• An estimated 15%–70% of international travelers returning to the United States have a travel-related illness. The likelihood of developing a medical condition during travel relates to an individual’s past medical history, travel destination, duration of travel, level of accommodation, pre-travel immunization history, adherence to prescribed malaria chemoprophylaxis regimens, activities during travel, and especially to his or her history of exposure to infectious agents prior to and during travel.
• While some illnesses that occur in returned travelers may begin during the travel period, others may occur weeks, months, or even years after return. In many cases, travelers may be harboring a pathogen in its incubation phase that becomes clinically evident in the immediate post-travel period. In terms of clinical severity, most travel-related illnesses are mild, but 1%–5% of travelers become sick enough to seek medical care either during or after travel. Thus, a history of travel, particularly within the previous 6 months, should be part of the routine medical history for every ill patient, especially those with a febrile illness.
• Particular groups of travelers are considered at higher risk of developing illness after returning to their place of residence. Travelers visiting friends and relatives are often less likely to seek pre-travel advice, obtain vaccinations, or take antimalarial prophylaxis. Adventure travelers and persons visiting friends and relatives overseas are at greater risk for becoming ill, in part because of increased exposure to pathogens.

Types of Illnesses

• The most frequent health problems in ill returned travelers are persistent gastrointestinal illness (10%), skin lesions or rashes (8%), respiratory infections (5%–13%, depending on season of travel), and fever (up to 3%).
• Although gastrointestinal upset is the most frequent problem, febrile illnesses represent the most serious of the spectrum of illnesses in travelers. Infections such as malaria may be life threatening, and others may pose a serious public health hazard (e.g., tuberculosis, measles, viral hemorrhagic fever).
• A recent analysis of the GeoSentinel Surveillance Network, a partnership of the International Society of Travel Medicine (www.istm.org) and CDC that gathers data from more than 30 travel and tropical medical clinics worldwide, has shown substantial regional differences in the morbidity of various syndromic categories in relation to place of exposure among ill returned travelers. For example, dermatologic problems were among the most frequent diagnoses among travelers returning from the Caribbean or Central or South America, while the diagnosis of acute diarrhea was more common for travelers returning from South Central Asia. Malaria was identified as one of the three most frequent causes of systemic febrile illness among travelers from any region. Other than malaria, travelers returning from sub-Saharan Africa were diagnosed most often with rickettsial infections, as well as typhoid and dengue.
• Fever is a frequently reported complaint among returned travelers. Recently, the GeoSentinel Surveillance Network reviewed its data on 24,920 travelers. This global surveillance system reported that 28% (6,957) of returned travelers seen at GeoSentinel clinics from March 1997 through March 2006 had fever as their chief reason for seeking medical care.
• Fever was a marker of a potentially serious illness in up to 26% of these travelers and often resulted in hospitalization. The most frequent “tropical” causes of fever in the returned traveler are malaria, dengue, invasive bacterial diarrhea, hepatitis A, typhoid, and rickettsial infections. However, nontropical entities such as respiratory or urinary tract infections account for a large proportion of febrile illnesses in returned travelers.
• In terms of gastrointestinal illnesses, acute bacterial gastroenteritis or parasitic diarrhea caused mostly by Giardia represents the most common conditions reported by travelers. Parasitic diarrhea may often present as intermittent diarrhea, nausea, headache, and fatigue, but may also present with postprandial rapid expulsions of loose stool. Rarely, postinfectious celiac sprue or postinfectious inflammatory bowel disease may occur after travelers have been ill with travelers’ diarrhea. More frequently, causes of persistent gastrointestinal illness are postinfectious irritable bowel syndrome and postinfectious lactose intolerance after an episode of travelers’ diarrhea.
• Although infections such as giardiasis or cyclosporiasis are often treated on the basis of clinical findings (without the benefit of laboratory confirmation), intestinal parasitic infections are uncommon causes of persistent diarrhea.
• Most post-travel skin ailments reported are insect bites, pyoderma, scabies, and cutaneous larva migrans.
• A number of diseases may occur months to years after return. The risk is related to the degree of exposure, the duration and season of travel, and the underlying health of the traveler. Some of these late-appearing illnesses include chronic forms of Chagas disease, cutaneous and mucocutaneous leishmaniasis, chronic forms of brucellosis, reactivation of tuberculosis from travel-acquired latent tuberculosis infection, malaria, sequelae of schistosomiasis, and reactivation of chronic systemic mycoses, such as paracoccidioidomycosis or coccidioidomycosis.

Clinical Presentations

• 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 (Table 4-1).
• 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 steps to ensure the patient has serial blood smears evaluated on the day of presentation 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; sexual contacts; and eating raw meat, seafood, or unpasteurized dairy products.
• Answers to these questions may provide important clues for diagnosis of a particular illness or syndrome in returned travelers. In addition, when an infectious disease is suspected, calculating an approximate incubation period is a useful step in ruling out possible etiologies. 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.
• Since most primary care physicians have little expertise in tropical diseases, a newly returned, ill international traveler should be preferentially evaluated by an infectious disease or tropical medicine practitioner. For assistance in finding a provider who practices clinical tropical medicine, access the American Society of Tropical Medicine and Hygiene website for a listing by state at www.astmh.org or the International Society of Travel Medicine at www.istm.org.

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