Clostridium difficile infection is a common healthcare-associated infection and one that is associated with significant morbidity as well as a risk for mortality. Current practice throughout the United States is targeted at infection prevention measures such as hand washing and isolation. Despite these measures, incidence of Clostridium difficile infections continue to rise as some institutions, including our own. Recently, a study published in Clinical Infectious Diseases found oral vancomycin for secondary prophylaxis to reduce the incidence of recurrence. No studies to date have evaluated primary prophylaxis with oral vancomycin. This will be a single center, prospective study to evaluate oral vancomycin use as primary Clostridium difficile prophylaxis. Patients treated by infectious disease physicians will be identified as "high risk" and after pager notification the ID physician will have the option to start oral vancomycin 125 mg by mouth daily if they determine it to be appropriate. Risk factors include age older than 65 years, taking gastric acid suppression medication, and receiving select broad-spectrum antibiotics. Oral vancomycin will be continued until de-escalation of antibiotics or hospital discharge and patients will be evaluated for Clostridium difficile infection development from the current hospital admission up to 4 weeks following antibiotic discontinuation.