Diarrhea.

The four major mechanisms of diarrhea are osmotic forces, secretory forces, exudation from a disrupted intestinal mucosa, and disturbed intestinal motility. In many illnesses, more than one mechanism produces diarrhea. The rotaviruses and the Norwalk viruses have recently been recognized as common causes of viral gastroenteritis. Also, the major cause of antibiotic-associated colitis is now known to be an overgrowth of Clostridium difficile. Campylobacter has also been identified as a common cause of acute bacterial diarrhea both abroad and in Canada. Most cases of travellers' diarrhea are caused by strains of Escherichia coli to which the traveller has little immunity. Most travellers who develop diarrhea benefit from treatment with diphenoxylate, loperamide or bismuth subsalicylate. The few patients who develop more severe, incapacitating diarrhea are candidates for treatment with trimethoprim-sulfamethoxazole. Antibiotics should not be used to prevent travellers' diarrhea, because antibiotic resistance is becoming a problem.