Assessment of Dientamoeba fragilis interhuman transmission by fecal microbiota transplantation.

Fecal microbiota transplantation (FMT) for recurrent Clostridioides difficile infection (rCDI) requires careful selection of stool donors to avoid transmitting pathogens. Dientamoeba fragilis detection remains an exclusion criterion based on its uncertain pathogenicity. The aim of this study was to assess D. fragilis interhuman transmission by FMT and its impact on the clinical success of rCDI. A retrospective study was conducted in rCDI patients from the COSMIC cohort undergoing FMT to investigate the potential transfer of D. fragilis from donor to recipient. The impact of FMT involving D. fragilis was also evaluated on the clinical outcomes of rCDI and adverse effects. This protist was found to be present in 15 out of 86 healthy donors screened (18.7%) who voluntarily took part in an FMT program. Examination of D. fragilis presence in stool samples from 17 patients both before and after FMT with D. fragilis-positive donations revealed no evidence of interhuman transmission through this process. Analysis of clinical outcomes and adverse events in 124 rCDI patients who underwent FMT (with 45 receiving D. fragilis-positive donations) showed no significant differences in success rates between patients receiving positive or negative D. fragilis transplants, 95.5% and 93.6%, respectively. No significant variances were observed in other side effects analyzed. These findings underscore the safety of using fecal transplant from D. fragilis positive donors in the FMT process. D. fragilis should be removed from the donor screening, which will represent a major improvement in the donor selection process from financial and practical standpoints.