C lostridium difficile (C. diff ) is the most common microbial cause of healthcare-associated infection in US hospitals and the leading cause of nosocomial diarrhea worldwide. The most common cause of C. diff infection is antibiotic exposure, which alters the balance of gut microbes, allowing for seeding and growth of C. diff , an anaerobic, toxin-producing bacterium. A recent Cochrane Review of 31 randomized controlled trials investigated the efficacy and safety of probiotics (any strain; any dose) as a preventative strategy for C. diff -associated diarrhea (CDAD) in adults and children.