Hydrogen-Positive Small Intestinal Bacterial Overgrowth (SIBO) in Japanese Patients With Chronic Intestinal...

Evidence for small intestinal bacterial overgrowth (SIBO) in chronic intestinal pseudo‑obstruction (CIPO) remains limited in Asian populations and by gas phenotype. This study aimed to determine the prevalence and gas phenotype distribution (hydrogen-positive SIBO vs. intestinal methanogen overgrowth) in Japanese patients with CIPO using glucose breath testing and to describe associated clinical features.

This single‑center cross‑sectional study was conducted at Niigata University, Niigata, Japan (April 2019-March 2022), and included 10 CIPO outpatients and 10 healthy controls. Participants fasted for 12 hours and avoided high-fiber foods for 24 hours before testing. Glucose breath testing (50 g, institutional SOP) measured hydrogen (H₂) and methane (CH₄); positivity followed North American Consensus criteria (ΔH₂ ≥20 ppm by 90 min; CH₄ ≥10 ppm). The primary outcome was hydrogen‑positive SIBO (H₂‑SIBO); intestinal methanogen overgrowth (IMO) was analyzed separately. Exact tests accounted for the small sample size.

H₂‑SIBO was more frequent in CIPO than in controls (5/10 vs. 0/10; Fisher two‑sided p = 0.0325; continuity‑corrected OR = 21). Overall SIBO (H₂ or CH₄) was 5/10 vs. 1/10 (p = 0.141, two‑sided). No CIPO patient met IMO criteria; one control was methane‑positive. Among CIPO patients, H₂‑SIBO was associated with lower BMI and a higher frequency of diarrhea.

In this small Japanese cohort, CIPO was associated with H₂‑SIBO, whereas IMO was uncommon. These findings should be interpreted with caution due to limited statistical power and potential under-detection of distal overgrowth with glucose substrate. These findings may inform on diagnostic strategies and nutritional management in severe motility disorders.