SER-262 Versus Placebo in Adults With Primary Clostridium Difficile Infection to Prevent Recurrence

Inclusion Criteria: 1. Signed informed consent, indicating that the subject understands the purpose of and procedures required for the study. 2. Male or female subjects ≥ 18 years. 3. A primary (first) episode of CDI with documentation of the episode including CDI date, test results, antibiotic treatment (including start and stop dates), and response to treatment Exclusion Criteria: 1. Females who are pregnant, breastfeeding, lactating, or planning to become pregnant during the study. 2. Known or suspected toxic megacolon and/or known small bowel ileus. 3. Active irritable bowel syndrome with diarrhea within the previous 12 months. 4. Major gastrointestinal surgery (eg, significant bowel resection or diversion) within 3 months before enrollment (this does not include appendectomy or cholecystectomy) or any history of total colectomy or bariatric surgery. 5. History of inflammatory bowel disease (ulcerative colitis, Crohn's disease, microscopic colitis) with diarrhea believed to be caused by active inflammatory bowel disease in the past 12 months. 6. Estimated glomerular filtration rate (eGFR) \< 60 ml/min/1.73m2 7. Admitted to or expected to be admitted to an intensive care unit for medical reasons (not just boarding). Patients discharged from an intensive care unit before Day 1 may be enrolled. 8. Concurrent intensive induction chemotherapy, radiotherapy, or biologic treatment for active malignancy (patients on maintenance chemotherapy may only be enrolled after consultation with medical monitor). 9. Absolute neutrophil count \< 500 cells/mm3