A Phase IIIB/IV Study to Compare the Efficacy of Vancomycin Therapy to Extended Duration of Fidaxomicin Therapy in the Clinical Cure of Clostridium Difficile Infection (CDI) in an Older Population

Inclusion Criteria: * CDI is confirmed by clinical symptoms (either \> 3 unformed bowel movements or ≥ 200ml of unformed stool (for subjects having rectal collection devices)) in the 24 hours prior to randomization and CDI test confirmed positive for presence of C. difficile toxin A or B in stool within 48 hr prior to randomization. * Subject agrees not to participate in another interventional study whilst participating in this study. Exclusion Criteria: * Subject is taking or requiring to be treated with prohibited medications * Subject has received more than one day of dosing of any therapy for CDI within the last 48 hours * Subject has experienced more than 2 previous episodes of CDI in the 3 months prior to study enrolment * Subject is unable to swallow oral study medication. * Subject has a current diagnosis of toxic megacolon. * Subject is not willing to adhere to the provisions of treatment and observation specified in the protocol. * Subject has been randomized into this study previously, has taken any investigational drug within 28 days or 5 half lives, whichever is longer, prior to enrollment, or is currently participating in another clinical study which may influence the assessment of efficacy and/or safety endpoints of this study, in the opinion of the Sponsor. * Subject has previously participated in a CDI vaccine study * Subject has hypersensitivity to fidaxomicin, vancomycin or any of its components.