Enteropathogens and Chronic Illness in Returning Travelers

Abstract

In 2011, approximately 980 million people traveled internationally.1 More than 522 million people from developed countries traveled overseas; an estimated 50 million to 100 million people traveled to developing countries.1-4 In 2007, the U.S. Department of Commerce estimated that at least 30 million Americans traveled to developing regions.4 Approximately 8% of travelers to the developing world require medical care during or after travel, and more than a quarter of those who seek medical assistance present with gastrointestinal symptoms.5-7 Although diarrhea occurs in up to 50% of people who travel to a developing country, it is only one of a number of infectious gastrointestinal illnesses that travelers may acquire.8-10 The broad spectrum of infectious gastrointestinal pathogens causing chronic illness in travelers, apart from travelers’ diarrhea,7,11,12 has not been well characterized. A recent study analyzed data from the GeoSentinel Surveillance Network (which consists of 42 specialized travel or tropical-medicine sites located around the world) on 25,867 returned travelers over a 9-year period (from 1996 to 2005).9 The analysis was performed on data from travelers who sought medical attention and not on the overall rates of gastrointestinal illness acquired during travel. The data showed that microbiologically confirmed gastrointestinal disease was diagnosed in approximately 30% (7442) of the travelers. Of the 2902 clinically significant pathogens that were isolated, approximately 65% were parasitic, 31% bacterial, and 3% viral. Six organisms (giardia, campylobacter, Entamoeba histolytica, shigella, strongyloides, and salmonella species) accounted for 70% of the gastrointestinal burden (Fig. 1). There were no diagnostic codes specifically for enterotoxigenic Escherichia coli, the most frequent cause of travelers’ diarrhea, or other commonly described pathogens, such as enteroaggregative E. coli, aeromonas, or plesiomonas.9 Coccidian parasites such as cyclospora, cryptosporidium, microsporidia, and isospora are increasingly recognized as causes of travelers’ diarrhea, but their percentages may have been underestimated in the GeoSentinel survey, since the diagnosis of these organisms requires specific staining techniques that are not routine in many laboratories.9 Similarly, viral pathogens, such as rotavirus and norovirus, are not routinely tested for at health centers, and their percentages could have been underestimated; however, these agents usually cause a short-term illness that typically resolves before travelers seek medical attention.9 The purpose of this review is to examine these enteropathogens that cause chronic and severe illness, as well as schistosoma (also known as the blood fluke, or bilharzia), which causes schistosomiasis, a common intravascular infection that is an increasingly recognized risk to travelers.13-15