Clostridium innocuum (CI) infection can lead to creeping fat in Crohn's disease and is associated with intestinal strictures. At present, no clinical study ever has evaluated the role of CI infection in inflammatory bowel disease (IBD).

In this retrospective cohort study, we enrolled hospitalized IBD patients with culture results for both CI and Clostridioides difficile (CD) in a medical center between October 2019 and April 2021. They were divided into the CI (CI+/CD−), control (CI−/CD−), coinfection (CI+/CD+), and CD (CI−/CD+) groups. We analyzed the risk factors, clinical presentations, and outcomes by comparing the CI and control groups.

We enrolled a total of 90 patients, including 22, 39, 13, and 16 patients in the CI, control, coinfection, and CD groups. The incidence rates of CI (CI+) and CD (CD+) were 39% (35/90) and 32% (29/90), respectively. We analyzed the differences between CI and control groups. We identified the use of steroid (77.3% vs. 46.2%, P = 0.018) and 5-aminosalicylic acid (90.9% vs. 64.1%, P = 0.022) as risk factors of CI infection. Clinical analysis showed that more patients in CI group presented with bloody stool (77.3% vs. 51.3%, P = 0.046). Although CI group had significantly lower overall occurrence of intraabdominal abscess (0% vs. 17.9%, P = 0.042), it showed a lower clinical remission rate (50% vs. 87.5%, P = 0.044) and higher Mayo score at the end of follow-up (10 points vs. 3 points, P = 0.008) in ulcerative colitis.

CI infection may lead to a poorer clinical remission in ulcerative colitis. We should take it into consideration in IBD patents with active inflamamtion or refractory diarrhea with or without CD infection. Precise identification of CI is imperative to guide approproate antimicrobial therapy because of its intrinsic vancomycin resistance nature.