Clinical Research Directory

Inclusion Criteria: * Inpatient or outpatient adults (≥18 years old) treated at the participating institutions. * First episode or first recurrence of CDI (i.e., second episode within 56 days) defined by a positive C. difficile assay (including PCR toxin gene detection, toxin enzyme immunoassay, and/or cell cytotoxicity neutralization assay37) and the presence of either ≥3 unformed stools in \<24 hours with a duration \>24 hours, endoscopic/histologic evidence of pseudomembranous colitis, or ileus. * Because of the prohibitive cost of fidaxomicin, the reimbursement criteria of fidaxomicin by the Régie de l'assurance maladie du Québec will be applied as inclusion criteria until dedicated fidaxomicin funding is available. This includes: either 1) ≥65 years old or immunosuppression, 2) a second episode of C. difficile within 12 weeks of a prior episode of C. difficile, or 3) multiply recurrent CDI (i.e., ≥2 recurrences). When additional funding is obtained, then only inclusion criteria 1 and 2 will be applied. Exclusion Criteria: * Planned or current treatment of the present episode of CDI with FMT, intravenous immunoglobulins, or other microbiome therapies (i.e., VOWST or REBYOTA). * Inability to take medications orally or crushed by tube. * Prior total colectomy. * Severe intolerance or allergy to oral vancomycin or fidaxomicin. * Patient is being admitted to a palliative care ward or is anticipated to die within 3 months of enrollment from another illness. * Fulminant CDI, defined according to the IDSA definition of CDI with the presence of hypotension, shock, ileus, and/or toxic megacolon. This is because vancomycin is generally preferred at this severity. * Receipt of more than 72 hours of off-study fidaxomicin or vancomycin CDI therapy for the current episode of CDI. * Pregnancy or planning to become pregnant during the study period because minimal data on fidaxomicin in pregnancy are available. * Active breastfeeding because minimal data on fidaxomicin in breastfeeding are available. * Prior enrollment in this trial. * Inability to consent without a healthcare proxy. * Lack of health insurance. * Anticipated transfer to a site not involved in this trial, or to a palliative care ward. * Patient declared anticipated inability to participate in study follow-up or lack of means for contact in the outpatient setting.