An investigational microbiome therapeutic composed of purified Firmicutes spores, SER-109, is superior to placebo for treatment of recurrent Clostridioides difficile infection, according to a study published in the New England Journal of Medicine. Paul Feuerstadt, MD, and colleagues randomized 182 patients who had three or more episodes of C. difficile infection to either SER-109 or placebo after standard-of-care antibiotics. The study team found that 12% and 40% of patients had recurrence of C. difficile infection in the SER-109 and placebo groups, respectively (relative risk [RR], 0.32) at up to 8 weeks of follow-up. In analyses stratified according to age, SER-109 led to less frequent recurrence than placebo (RRs, 0.24 and 0.36 for those younger than 65 and those aged 65 and older, respectively); results were similar in analyses stratified according to antibiotic received (RRs, 0.41 and 0.09 for vancomycin and fidaxomicin, respectively). The number of adverse events, which were mostly mild-to-moderate and gastrointestinal in nature, was similar in the two groups.