A Comparison of Fidaxomicin and Vancomycin in Patients With CDI Receiving Antibiotics for Concurrent Infections

Inclusion Criteria: * Patients 18 years of age or older with \>3 unformed stools/24 hours with positive stool test for C. difficile. * Patients receiving ≥ 1 high or medium risk antibiotic for treatment of an infection other than CDI, for an anticipated duration of ≥ 5 days from the time of enrollment. * High risk: carbapenems, 2nd-4th generation cephalosporins, fluoroquinolones, clindamycin, and beta-lactam/beta-lactamase inhibitor combinations * Medium risk: 1st generation cephalosporin, macrolides\*, and aztreonam * \*The macrolide would be considered to be low risk if patients are receiving intermittent macrolides for prophylaxis only and not for treatment of an acute infection Exclusion Criteria: * Patients with severe-complicated disease that would compromise oral therapy (hypotenstion or shock, ileus or bowel obstruction, megacolon). * Patients with an allergy to oral vancomycin or fidaxomicin. * Patients anticipated to receive metronidazole after enrollment. * Patients who already received oral vancomycin or metronidazole (either oral or intravenous) for \> 24 hours within the preceding 72 hours at the time of enrollment. * Patients anticipated to receive adjunctive C. difficile therapy (rifaxamin, nitazoxanide, tigecycline) after enrollment. * Patients who are on laxatives before they are enrolled into the study, such as lactulose, if: * Patients have had a recent dose adjustment; * Baseline number of bowel movement while on laxatives is unknown. * Number of bowel movements and/or consistency has not changed from baseline. * Patients who have had colostomy or ileostomy * Patients who will have colostomy or ileostomy after enrollment and before study ends * Patients who are or will be on long-term (\>12 weeks) medium or high-risk antibiotics prophylaxis after enrollment