Blastocystis spp. in fecal microbiota transplantation: Evidence, policy, and the screening paradox

Fecal microbiota transplantation (FMT) is an established treatment for recurrent Clostridioides difficile infection (rCDI). However, the detection of Blastocystis spp. in potential donors remains controversial and often leads to donor exclusion, despite uncertain pathogenicity. This review aims to critically evaluate the available evidence on Blastocystis spp. transmission through FMT, its clinical impact, and the implications of current donor screening strategies.

A narrative review of the literature was performed using PubMed, Embase, and Web of Science. Studies reporting Blastocystis spp. detection in FMT donors or recipients, transmission events, clinical outcomes, diagnostic methods, and microbiome associations were included and analyzed.

Across published reports, 34 FMT recipients were exposed to Blastocystis spp.-positive donor material. Transmission was limited to common subtypes (ST1-ST3), was transient, and was not associated with adverse clinical outcomes or reduced efficacy of FMT for rCDI. No cases of symptomatic infection were reported. Frozen stool preparations appeared to abolish parasite viability. Molecular screening methods markedly increased detection rates compared with microscopy, frequently identifying low-burden colonization of uncertain clinical relevance. Available data suggest that Blastocystis spp. carriage may coexist with a healthy microbiome and does not negatively impact FMT outcomes.

Current evidence indicates that Blastocystis spp. transmission through FMT in immunocompetent adults is clinically benign. Routine donor exclusion based solely on Blastocystis spp. detection may therefore be overly restrictive. A risk-based approach incorporating parasite burden, subtype, host factors, and processing methods may better balance patient safety with donor availability, supporting more sustainable FMT programs.