Clinical considerations in the diagnosis of antimicrobial agent-associated gastroenteritis.

Most gastrointestinal infections secondary to the use of antimicrobial agents that have been documented are related to overgrowth of Clostridium difficile which produces a spectrum from severe pseudomembranous colitis to mild diarrhea or asymptomatic carriage. The most common inducers of pseudomembranous colitis or antimicrobial agent-associated diarrhea are ampicillin, clindamycin, and various cephalosporins, but almost all antimicrobials may cause this problem. Symptoms vary from watery to bloody diarrhea; the extent and severity of the diarrhea, fever, and abdominal cramps and the incidence of complications (such as toxic megacolon and perforation of the bowel) and of fatality are variable. Normal carriage of C. difficile in infants and asymptomatic carriage in adults who have received antimicrobial therapy make it impossible to rely on culture for diagnosis. The presence of cytotoxin or enterotoxin produced by C. difficile is much more reliable diagnostically, but there may be false-positives with this as well, particularly in infants. However, the combination of the appropriate clinical picture and background and presence of toxin usually permit accurate diagnosis. The definitive method of diagnosis, often not feasible to employ, is demonstration by colonoscopy or sigmoidoscopy of the pathognomonic yellow, elevated plaques on the colonic mucosa. Colonoscopy is preferred since the plaques may be restricted to the right colon, particularly in early cases. From the practical standpoint, the best diagnostic test is demonstration of C. difficile toxin.