Screening to Prophylax Against Clostridium Difficile Infection -

Inclusion Criteria: 1. Expected duration of admission sufficient to complete screening and enrollment 2. Age ≥18 3. Able to give informed consent 4. Initiated on one of the following antibiotics within the prior 72 hours with an expected duration of at least 72 hours from enrollment: clindamycin, ampicillin, ampicillin/sulbactam, amoxicillin, amoxicillin/clavulanate, moxifloxacin, levofloxacin, piperacillin/tazobactam, or any cephalosporin 5. Maximum expected duration of antibiotics 8 weeks 6. Able to take oral study medications 7. Able to provide a stool sample during hospitalization or within 3 days of discharge 8. Reasonably expected to be able to complete follow up Exclusion Criteria: 1. Chron's disease, ulcerative colitis, celiac disease, or other chronic diarrheal illness 2. CDI within prior 90 days 3. Currently on metronidazole, oral vancomycin, rifaximin, fidaxomicin, or any other antibiotic active against C. difficile 4. Current diarrhea 5. Current ileostomy, colostomy or other form of surgically disconnected gut such that oral therapy would not be expected to reach the entire lumen of the gut 6. Pregnancy or breast feeding (determined prior to randomization) 7. Travel to an area of endemic diarrheal illness within the last 30 days 8. Life expectancy of less than 60 days 9. Known allergy to vancomycin 10. Participation with other research trials that could impact the results of this trial within the last 30 days 11. Previously enrolled in this study