Small intestinal bacterial overgrowth (SIBO) is prevalent in irritable bowel syndrome (IBS), but its’ association with other functional gastrointestinal disorders (FGIDs) is less certain. This study aimed to explore SIBO in a multi-racial Asian population with various FGIDs compared to non-FGID controls.
Consecutive Asian adults with Rome III diagnosed common FGIDs (functional dyspepsia/FD, IBS and functional constipation/FC) and non-FGID controls were subjected to glucose breath testing, with hydrogen (H2) and methane (CH4) levels determined.
A total of 244 participants (FGIDs n = 186, controls n = 58, median age 45 years, males 36%, Malay ethnicity 76%) were recruited. FGIDs had a higher prevalence trend of SIBO compared to controls (16% FGIDs vs. 10% controls, p = 0.278) with 14% in FD, 18% in IBS and 17% in FC. Compared to controls, SIBO was associated with diarrhoea-predominant IBS (IBS-D) (24% vs. 10%, P = 0.050) but not with other types of FGIDs. IBS-D remained an independent predictor of SIBO (OR = 2.864, 95% CI 1.160-7.071, p = 0.023) but not PPI usage nor history of diabetes (both p > 0.050) at multivariate analysis. Compared to controls, SIBO in IBS-D was associated with an elevated H level (≥ 20 ppm from baseline) (18% vs. 3%, p = 0.017), but not CH4 levels (≥ 10 ppm) (9% vs. 7%, p = 0.493). In addition, no difference was found in the prevalence of methane-positive SIBO between chronic constipation (constipation-predominant IBS and FC) compared to controls (9% vs. 7%, P = 0.466).
SIBO is prevalent amongst multi-ethnic Asian adults with and without FGIDs. Amongst various FGIDs, only IBS-D is significantly associated with SIBO.

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