Small intestinal bacterial overgrowth linked to irritable bowel syndrome

An association appears to exist between irritable bowel syndrome (IBS) and small intestinal bacterial overgrowth (SIBO), suggest the results of a systematic review and meta-analysis. However, the overall quality of evidence is low.

“This is mainly due to substantial ‘clinical heterogeneity’ due to lack of uniform selection criteria for cases and controls and limited sensitivity and specificity of the available diagnostic tests,” the investigators said.

Studies reporting SIBO prevalence in IBS patients were identified through electronic database searches up to December 2018. The investigators calculated prevalence rates, odds ratios (ORs) and 95 percent confidence intervals (CIs) of SIBO in IBS patients.

Twenty-five studies comprising 3,192 patients with IBS and 3,320 controls met the eligibility criteria. SIBO prevalence was significantly greater in IBS patients compared with controls (OR, 3.7, 95 percent CI, 2.3–6.0). In studies with only healthy controls, SIBO in IBS patients showed a much higher OR at 4.9 (95 percent CI, 2.8–8.6).

SIBO prevalence diagnosed by breath test remained higher in IBS patients (35.5 percent, 95 percent CI, 33.6–37.4) than in controls (29.7 percent, 95 percent CI, 27.6–31.8).

In culture-based studies, SIBO prevalence was 13.9 percent (95 percent CI, 11.5–16.4) in IBS patients and 5.0 percent (95 percent CI, 3.9–6.2) in controls with a cutoff value of 10⁵ colony-forming units per millilitre compared with 33.5 percent (95 percent CI, 30.1–36.9) in IBS patients and 8.2 percent (95 percent CI, 6.8–9.6) in controls with a cutoff value of 10³ colony-forming unit per millilitre.

SIBO prevalence was much greater in both patients with IBS (3.6-fold) and controls (7.6-fold) on lactulose vs glucose breath tests. Difference was comparable when lactulose breath test was compared with culture methods.

SIBO in patients with IBS-diarrhoea vs IBS-constipation had an OR of 1.86 (95 percent CI, 1.83–2.8). Methane-positive breath tests were significantly more prevalent in IBS-constipation vs IBS-diarrhoea (OR, 2.3, 95 percent CI, 1.2–4.2).

In addition, use of proton pump inhibitors did not correlate with SIBO in patients with IBS (OR, 0.8, 95 percent, 0.5–1.5; p=0.55).