Which pathogens are the most common causes of traveler's diarrhea and what are their typical transmission routes?

• A. Enterotoxigenic E. coli (ETEC) is most common; others include EAEC, Shigella, and Campylobacter; transmitted via contaminated food and water
• B. Enteropathogenic E. coli is most common; transmitted via airborne particles
• C. Salmonella is the most common; transmitted via contaminated food only
• D. Norovirus is the most common bacterial cause; transmitted via water

Answer: (A)

Traveler's diarrhea is driven by bacteria acquired through ingestion of contaminated food or water while traveling. The leading organism is enterotoxigenic E. coli, which releases toxins that provoke secretory, watery diarrhea. Its prominence comes from easy fecal–oral transmission in many travel destinations—think street foods, unpurified water or ice, and other contaminated sources—and from its low infectious dose, so even small exposures can cause illness. Other common bacterial contributors include enteroaggregative E. coli, Shigella, and Campylobacter. EAEC often causes watery to mucoid or even persistent diarrhea and is transmitted via contaminated food and water; Shigella and Campylobacter are also spread by the fecal–oral route, frequently through contaminated food or water and, for Shigella, person-to-person spread. Enteropathogenic E. coli is less typical as a cause of traveler's diarrhea in adults, and while Salmonella can cause traveler's diarrhea, it is not as consistently the most common culprit as ETEC. Norovirus is a major cause of gastroenteritis overall but is viral, not the primary bacterial cause of traveler's diarrhea, and the emphasis here is on the common bacterial pathogens and their fecal–oral transmission via contaminated food and water.