Inclusion Criteria

• ≥ 18 years old.
• Medical record documentation of recurrent CDI, defined as at least one recurrence after a primary episode and has completed at least two rounds of standard-of-care oral antibiotic therapy. Study subjects will have their diarrhea resolved, i.e., would be having less than 3 watery bowel movements at the time of study enrollment for 48 hours or more.
• A positive stool test for the presence of C. difficile within 30 days prior to enrollment and standard C. difficile treatment.
• Willing and able to swallow capsules.
• Agrees to abstain from non-dietary probiotics for the duration of the study.
• Agrees to abstain from vancomycin, metronidazole, fidaxomicin, rifaximin, nitazoxanide and IVIG for the duration of the study unless prescribed to treat recurrent CDI.
• Agrees to stop proton pump inhibitors or H2 blocker medications.
• Agrees to practice a form of effective contraception during study participation.
• Has a negative urine pregnancy test at the time of enrollment (females of child-bearing potential only).
• Willing and able to provide informed consent and HIPAA authorization.
• Willing and able to complete the required Subject Diary.
• Willing and able to meet all study requirements, including attending all assessment visits and phone calls

Exclusion Criteria

• A known history of continued CDI diarrhea, despite being on a course of antibiotics prescribed for CDI treatment.
• Requires continuous antibiotic therapy for a condition other than CDI.
• Previous fecal transplant.
• Previous treatment with RBX2660.
• Diagnosis of irritable bowel syndrome (IBS) as determined by Rome III criteria.
• History of chronic diarrhea.
• History of celiac disease.
• Disease symptoms caused by a confirmed intestinal pathogen other than C. difficile.
• Unable to stop proton pump inhibitors or H2 blocker medications.
• Intra-abdominal surgery within the last 60 days.
• Evidence of active, severe colitis.
• History of short gut syndrome.
• Requires the regular use of medications to manage bowel hypermotility.
• Planned therapy in the next 3 months that may cause diarrhea (e.g., chemotherapy).
• Planned surgery requiring perioperative antibiotics within 3 months of study enrollment.
• Life expectancy of < 6 months.
• Compromised immune system (e.g., HIV infection; AIDS-defining diagnosis or CD4 <200/mm3; inherited/primary immune disorders; immunodeficient or immunosuppressed due to a medical condition or medication; current or recent (< 90 days) treatment with chemotherapy; or current or recent (< 90 days) treatment with immunosuppressant medications.
• Taking systemic steroids (≥ 20 mg a day or prednisone-equivalent) or is expected to be on steroids after enrollment through 8 weeks after completing the assigned study treatment.
• An absolute neutrophil count of <1000 cells/µL.
• Known or suspected current (< 90 days) illicit drug use.  Note:  marijuana use is allowed.
• Pregnant, breastfeeding, or intends to become pregnant during study participation.
• Participating in a clinical trial of another investigational product (drug, device or other) and has not completed the required follow-up period.
• Subject, in the opinion of the investigator, for whatever reason, should be excluded from the study.