Small Intestinal Bacterial Overgrowth in Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis of Case-Control Studies

Shah A1,2,3, Talley NJ4, Jones M5, Kendall BJ1,2, Koloski N1,4, Walker MM4, Morrison M1,2,6, Holtmann GJ1,2,3. Am J Gastroenterol. 2020 Jan 6. doi: 10.14309/ajg.0000000000000504. [Epub ahead of print]


Author information

Faculty of Medicine & Faculty of Health and Behavioural Sciences, The University of Queensland, Brisbane, Queensland, Australia.

Department of Gastroenterology and Hepatology, Princess Alexandra Hospital, Brisbane, Queensland, Australia.

Translational Research Institute, Brisbane, Queensland, Australia.

Faculty of Health and Medicine, The University of Newcastle, Newcastle, New South Wales, Australia.

Department of Psychology, Macquarie University, Sydney, New South Wales, Australia.

University of Queensland, Diamantina Institute, Brisbane, Queensland, Australia.


INTRODUCTION: We conducted a systematic review and meta-analysis to compare the prevalence of small intestinal bacterial overgrowth (SIBO) in patients with irritable bowel syndrome (IBS) and controls.

METHODS: Electronic databases were searched up to December 2018 for studies reporting SIBO prevalence in patients with IBS. Prevalence rates, odds ratios (ORs), and 95% confidence intervals (CIs) of SIBO in patients with IBS and controls were calculated.

RESULTS: We included 25 studies with 3,192 patients with IBS and 3,320 controls. SIBO prevalence in patients with IBS was significantly increased compared with controls (OR = 3.7, 95% CI 2.3-6.0). In studies using only healthy controls, the OR for SIBO in patients with IBS was 4.9 (95% CI 2.8-8.6). With breath testing, SIBO prevalence in patients with IBS was 35.5% (95% CI 33.6-37.4) vs 29.7% (95% CI 27.6-31.8) in controls. Culture-based studies yielded a SIBO prevalence of 13.9% (95% CI 11.5-16.4) in patients with IBS and 5.0% (95% CI 3.9-6.2) in controls with a cutoff value of 10 colony-forming units per milliliter vs 33.5% (95% CI 30.1-36.9) in patients with IBS and 8.2% (95% CI 6.8-9.6) in controls with a cutoff value of 10 colony-forming unit per milliliter, respectively. SIBO prevalence diagnosed by lactulose breath test is much greater in both patients with IBS (3.6-fold) and controls (7.6-fold) compared with glucose breath test. Similar difference is seen when lactulose breath test is compared with culture methods. OR for SIBO in patients with IBS-diarrhea compared with IBS-constipation was 1.86 (95% CI 1.83-2.8). Methane-positive breath tests were significantly more prevalent in IBS-constipation compared with IBS-diarrhea (OR = 2.3, 95% CI 1.2-4.2). In patients with IBS, proton pump inhibitor was not associated with SIBO (OR = 0.8, 95% CI 0.5-1.5, P = 0.55).

DISCUSSION: This systematic review and meta-analysis suggests a link between IBS and SIBO. However, the overall quality of the 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.

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