Diarrhea is defined as watery or liquid stools, usually with increases in daily frequency and in total stool weight (i.e., more than 200 g per day). The pathogens that commonly cause sporadic diarrhea in adults in developed countries are Campylobacter, Salmonella and Shigella species; Escherichia coli; Yersinia species; protozoa; and viruses. However, pathogens are not detected in more than one half of cases. Traveler's diarrhea is caused by bacteria in about 80 percent of patients. Common pathogens are enterogenic E. coli, Salmonella, Shigella, Campylobacter, and Vibrio, Yersinia and Aeromonas species. Death from diarrhea is rare, but persons older than 74 years and those in long-term care facilities are at greater risk. De Bruyn reviewed the literature for controlled trials that evaluated the efficacy of empiric antibiotic treatment of diarrhea.

The goals of treatment include reducing the infectious period, length of illness, risk of transmission to others, risk of dehydration and rates of severe illness. Empiric treatment of traveler's diarrhea shortened the length of illness, although it was occasionally associated with prolonged presence of the causative pathogen in the stool and the development of resistant strains. Adverse effects varied by agent, but gastrointestinal symptoms such as cramps, nausea and anorexia, dermatologic symptoms such as rash, and respiratory symptoms such as cough and sore throat were commonly reported. Empiric treatment of community-acquired diarrhea with ciprofloxacin shortened the length of illness by one to two days. Development of resistant strains occurred with the use of some antibiotics but not with others. Adverse effects were similar to those noted for traveler's diarrhea.

The author concludes that the various pathogens responsible for diarrhea respond to antibiotics in a variety of ways. In traveler's diarrhea, empiric treatment with antibiotics reduces the length of illness by one to two days. In community-acquired diarrhea, ciprofloxacin similarly reduces the duration of diarrhea. Other agents were not successful in treating this type of diarrhea. Treatment also tends to prolong the excretion of organisms in the stool and is associated with the development of resistant organisms.

editor's note: Identifying patients with ambulatory diarrhea who require antibiotic treatment is a vexing problem. In a related article, Herbert points out the lack of correlation of white blood cells in the stool with positive stool cultures. In addition, neither the stool culture results nor the fecal white blood cell count predicts the response to therapy for domestic or imported diarrhea.

Drug prophylaxis for prevention of traveler's diarrhea is now discouraged because of the widespread problem of antibiotic resistance. Therefore, antibiotic treatment is best reserved for use in patients who do not respond to hydration and treatment with anti-diarrheals such as loperamide. A good review of the prevention and treatment of traveler's diarrhea appears in an article published in American Family Physician (1999;60:119–24, 135–6).—r.s.