Diarrhea is the most frequent health problem encountered by persons going from industrialized to developing countries. From the 50 million people traveling annually, approximately 40% will suffer from so-called travelers' diarrhea (TD) at least once.

Classically, TD is defined as the passage of three or more unformed stools within 24 hours in association with at least one of the following symptoms of enteric infection: nausea, vomiting, abdominal pain or cramps, fever, fecal urgency, tenesmus, or the passage of bloody/mucoid (dysenteric) stools. This definition includes illness occurring up to 10 days after travelers return to their home countries.

Cases of TD can be categorized by severity as being mild (no disturbance in normal activities), moderate (modii ed travel activities required), or severe (illness requires confinement to bed). Fewer than 1% of patients are admitted to a hospital, but almost 40% are required to change their travel schedule.

Acute TD lasts for less than 2 weeks. Illness lasting more than 2 weeks is considered “persistent” and is seen in 2% to 10% of travelers. Possible etiologies of persistent diarrhea include intestinal infection by protozoal parasites, for example, giardiasis or cryptosporidiosis, and occasionally bacterial enteropathogens can cause a more protracted diarrhea. Unmasked gastrointestinal disease is seen in this setting occasionally, including celiac sprue, inflammatory bowel disease, and malabsorptive syndromes. Postinfectious irritable bowel syndrome has been shown to occur in as many as 10% of people after an episode of TD.