This is a prospective, multicenter, randomized, double-blinded, placebo-controlled Phase 3 study of a microbiota suspension of intestinal microbes. Patients who have had at least two recurrences after a primary episode and have completed at least two rounds of standard-of-care oral antibiotic therapy or have had at least two episodes of severe CDI resulting in hospitalization within the last year may be eligible for the study. Subjects who are deemed failures following the blinded treatment per the pre-specified treatment failure definition may elect to receive an unblinded RBX2660 enema.