Poop Transplants Work in Kids With Recurrent C. difficile. For Everything Else, It’s Complicated.

Fecal microbiota transplantation (FMT), the practice of transferring stool from a healthy donor into a sick recipient to rebuild a disrupted gut ecosystem, has earned a firm foothold in adult medicine. Now a comprehensive 2026 review in Microorganisms, drawing on 113 publications and covering patients from birth to 18 years, maps out where the therapy genuinely works in children and where enthusiasm still outpaces the data.

FMT Clears Recurrent C. difficile in Over 80% of Pediatric Cases

The clearest win is against recurrent Clostridioides difficile infection (rCDI), a condition in which gut dysbiosis and impaired immune responses let the bacterium reestablish itself within 60 days of antibiotic therapy. For children who have already failed standard antibiotic regimens, a single FMT procedure resolves infection in roughly 81% of cases; a second procedure pushes that figure to nearly 90%. Both the North American and European pediatric gastroenterology societies (NASPGHAN and ESPGHAN) now recommend FMT for pediatric rCDI after antibiotic failure, placing it among a small number of interventions with genuine guideline backing in this age group. A prior meta-analysis of FMT for pediatric C. difficile put the pooled success rate at 86% overall, though efficacy dipped to 75% in children who also had inflammatory bowel disease, a finding that hints at how underlying gut pathology complicates outcomes.

Unlike conventional probiotics, which deliver one or a handful of microbial strains, FMT transfers a dense consortium of organisms, metabolites, and microbial-derived proteins. That complexity is precisely the point: rCDI is driven by the collapse of the competing microbial community that normally holds C. difficile in check, and rebuilding that community requires more than a single species can provide.

Why Immunocompromised Children Present a Harder Problem

Pediatric oncology patients, transplant recipients, and children with inflammatory bowel disease make up a disproportionate share of CDI cases, and they are also the patients for whom FMT carries the most uncertainty. Cancer-related factors, including chemotherapy, frequent antibiotic courses, and mucosal barrier damage, accelerate microbial collapse. In children with hematological malignancies, reduced gut microbial diversity during the peri-transplant period is linked to higher rates of graft-versus-host disease (GvHD), delayed neutrophil recovery, and bloodstream infections.

FMT has been explored as a way to reconstitute the microbiome after hematopoietic stem cell transplantation (HSCT) and to reduce GvHD severity, with preliminary case series suggesting microbiota reconstitution is achievable. One small series reported successful decolonization of multidrug-resistant organisms in children undergoing HSCT. Yet current clinical practice guidelines from 2018 and 2024 advise against routine FMT in immunocompromised pediatric patients, citing limited data and genuine safety concerns: while adverse events from FMT are usually mild (abdominal discomfort, transient diarrhea, bloating), bacteremia and sepsis, though rare, have been reported, and the risk profile rises steeply in children whose immune systems cannot contain an unexpected pathogen.

In pediatric rCDI specifically among oncology patients, responses were heterogeneous: in one reported cohort of four patients, two resolved after a single FMT, one required six procedures, and outcomes were inconsistent.

How the Review Assembled Its Evidence

The Zambelli team conducted a systematic search across PubMed/MEDLINE, Scopus, Web of Science, and the Cochrane Library from inception through December 2025. Two independent reviewers screened titles, abstracts, and full texts, with a third reviewer resolving disagreements. The final corpus of 113 publications included randomized controlled trials, prospective and retrospective cohort studies, case series, systematic reviews, and clinical guidelines. The pediatric population was defined as birth to under 18 years, with particular attention to infants and toddlers aged three and under.

That scope reveals a structural problem: randomized controlled trials in pediatric populations are scarce. Most available evidence derives from observational studies or single-center cohorts with narrow indications. Heterogeneity in how FMT is prepared and delivered complicates comparison across studies. Administration routes include oral capsules, nasoenteric infusion, enemas, and colonoscopy; colonoscopy is the most studied and upper gastrointestinal routes are associated with more frequent adverse events. Donors are typically screened with medical history questionnaires and same-day eligibility checks, with age-matched donors linked to lower incidence of adverse events.

Open Questions About FMT in IBD, Autism, and Functional Disorders

Beyond rCDI, the review characterizes every other pediatric application as investigational. For ulcerative colitis, pooled analyses (largely from adult data) show remission rates of 37% with FMT versus 18% in controls, but pediatric-specific data are sparse and long-term outcomes are essentially unknown. Evidence for Crohn's disease is described as extremely limited and inconclusive; the PediCRaFT randomized trial, which enrolled children aged 12 and older with Crohn's disease, represents the kind of rigorous design needed but is not yet available to change practice.

For neurodevelopmental conditions, particularly autism spectrum disorder (ASD), one open-label study reported significant improvements in both gastrointestinal and behavioral symptoms following a modified FMT protocol called microbiota transfer therapy, which includes antibiotic pre-treatment, bowel cleansing, and a prolonged course of microbiota administration. The result is intriguing given the well-documented gut-brain connections in ASD research, but the study's small sample size, short follow-up, and susceptibility to placebo response mean it falls well short of practice-changing evidence.

Functional disorders such as constipation and irritable bowel syndrome fare no better in terms of evidence quality: most data come from small, uncontrolled studies or adult cohorts, and outcomes in children are inconsistent.

Where Pediatric FMT Research Needs to Go Next

The review's clearest message for the research community is a call for multicenter randomized controlled trials designed specifically for children. Systematic exclusion of pediatric oncology patients from existing trials has forced clinicians to rely on adult-derived or indirect evidence for some of the highest-need patients. Standardizing FMT preparation, dosing, timing, and delivery route across studies would make future evidence interpretable in ways the current literature is not.

Longer follow-up is essential, particularly in immunocompromised children where long-term safety data are almost entirely absent. Researchers are also looking beyond the gut: future directions for pediatric FMT include potential applications in autoimmune conditions such as type 1 diabetes and neurological disorders like multiple sclerosis, areas where the gut-immune axis is increasingly implicated but where FMT evidence is even earlier-stage than in IBD or ASD.

For now, the practical takeaway is straightforward: FMT is a genuine tool for children who keep getting C. difficile despite antibiotics, and it works well enough that society guidelines back it. For nearly everything else on the investigational list, the biology is compelling, the early signals are sometimes promising, and the rigorous evidence is still being built.

Evidence rating

EMERGING — 84/100

Caveats:

• This is a narrative/systematic review synthesizing existing literature — it does not generate new trial data of its own.
• For most indications beyond recurrent C. difficile infection, the underlying evidence base consists of small, single-center observational studies or adult data extrapolated to children.
• Long-term safety data for pediatric FMT, especially in immunocompromised patients, are insufficient.
• Substantial variability in donor screening, preparation, dosing, and delivery routes across studies limits direct comparisons and standardization.
• Funding source was not disclosed by the authors.

Systematic review synthesizing 113 publications (RCTs, cohort studies, meta-analyses, and guidelines) on FMT in pediatric populations up to age 18. Evidence for recurrent C. difficile infection is supported by multiple studies showing consistent >80% success rates, but for most other indications the underlying trials are small, non-randomized, and largely single-center, limiting causal conclusions. Long-term safety and efficacy data remain insufficient, particularly for immunocompromised children, and have not yet been independently replicated at scale in dedicated pediatric RCTs.