Case Report: Allergic reaction following fecal microbiota transplantation in children with autism spectrum disorder: a report of two cases.

Background: Fecal microbiota transplantation (FMT) is increasingly used in children with autism spectrum disorder (ASD) and is generally considered to have an acceptable safety profile. However, the risk and mechanisms of severe adverse events in the high-risk subgroup of children with ASD complicated by multiple food intolerances (FI) have not been reported, and clinical strategies for risk prevention and management remain lacking. Case report: This article reports two cases of children with ASD and multiple FIs who developed anaphylactic shock following FMT, representing the first such report in the pediatric field. Case 1 presented with early-stage shock, which was considered to be associated with IgG-mediated type III hypersensitivity. Case 2 developed classic anaphylactic shock with a biphasic course characterized by relapse after initial resolution, raising the possibility of biphasic anaphylaxis. Both children improved after standardized anti-allergy and anti-shock treatment, and one child successfully completed subsequent FMT using a low-dose regimen. Conclusion: FMT carries a risk of anaphylactic shock in children with ASD and multiple FIs, who have underlying susceptibility due to impaired intestinal barrier function and immune dysregulation. Refined risk stratification, close monitoring throughout the procedure, individualized transplantation protocols, and standardized emergency procedures can effectively enhance the safety and feasibility of FMT in this high-risk subgroup.