Many studies have been published indicating a potential for probiotics as a prophylaxis against diarrhea associated with antibiotic use in humans. Additionally, a recent report in a rodent model suggests that kefir consumption concomitantly with antibiotic treatment may prevent the development of C. difficile-associated diarrhea. However, to our knowledge there have not been any studies published that have investigated the preventive effects of kefir consumption specifically related C. difficile infection in human patients. This protocol will serve as an initial study for a subset of at-risk patients and the data collected will provide guidance for future studies to include a more broad range of at-risk patients.