Diarrhea is a relatively common complication of antibiotic use. Nearly all agents with an antibiotic spectrum of activity have been implicated. The great majority of cases are either enigmatic or caused by Clostridium difficile.

DIAGNOSTIC STUDIES

Clostridium difficile–associated disease should be suspected in any patient who has diarrhea in association with antibiotic exposure. The most common inducing agents are clindamycin, fluoroquinolones, and cephalosporins. Nevertheless, nearly any antimicrobial agent with an antibacterial spectrum of activity can cause this complication.

The usual method for identifying cases of diarrhea caused by C. difficile is the toxin assay. The original technique was with a tissue culture assay for detection of cytotoxin or toxin B; more recently 95% of laboratories in the United States have used the enzyme immunoassay (EIA) for detection of toxin A or toxin A plus B. Occasional labs screen for C. difficile by culture (which takes 3 days) or by detecting the common antigen (which takes hours) to be followed by testing for the toxin by the more sensitive tissue culture method. Studies of the EIA compared with the tissue culture assay indicate that it is relatively specific and has the advantage of providing results within 2 to 3 hours, but it is only about 75% sensitive, so there are many false negatives.

Anatomic studies, usually sigmoidoscopy or colonoscopy, were far more common before the general availability of C. difficile toxin assays in the late 1970s.