Clostridium difficile infection (CDI) is an anaerobic spore-forming bacillus that colonizes the intestinal tract in patients whose normal gut microbiota is disrupted by antibiotic therapy or for any other reason. C difficile produces two major toxins—toxins A and B—that cause intestinal mucosal injury, diarrhea, and colitis. In some cases, fulminant infection leads to shock, ileus, and toxic megacolon. In high-income countries, C. difficile is the most common cause of infectious diarrhea in hosp