The purpose of this study is to learn about the safety of RBX2660 and whether it is effective in preventing recurrent Clostridium difficile infection (CDI). This study involves an investigational new drug called RBX2660. An investigational new drug is a drug that is tested in people and has not been approved for sale by the United States Food and Drug Administration (FDA). RBX2660 is a microbiota suspension. A microbiota suspension is a biologic product (a product made from living cells) thought to prevent recurrent CDI by restoring the normal balance of microorganisms in the intestines through the transplant of live, beneficial microorganisms. It is believed that CDI is caused by a disruption of the normal, healthy balance of microorganisms (tiny living cells) in the intestine (gut or bowel) after taking antibiotics. Many people with CDI are cured with another course of antibiotics, but there are a number of people who develop chronic (ongoing) CDI with repeated bouts of severe diarrhea that are only resolved while the person is taking antibiotics; when the antibiotics are stopped, the diarrhea returns. Therefore, Rebiotix has developed RBX2660 to help prevent CDI infections from returning in people with recurrent CDI.