Review Article

Small Intestinal Bacterial Overgrowth

Prevalence, Clinical Features, Current and Developing Diagnostic Tests, and Treatment

E. Grace; C. Shaw; K. Whelan; H. J. N. Andreyev


Aliment Pharmacol Ther. 2013;38(7):674-688. 

In This Article

Small Intestinal Bacterial Overgrowth and IBS

In many conditions, it can be difficult to assess whether SIBO is a cause for the GI symptoms and/or malabsorption or whether these occur as a result of a primary disease and SIBO is just an epiphenomenon.[19,68] In this regard, SIBO as the aetiology or as a bystander in IBS has received the most attention. There is a definite overlap between the symptoms that define IBS[69] and those which are typical of SIBO (e.g. abdominal pain, bloating, flatulence, diarrhoea and/or constipation).

A systematic review and meta-analysis of studies investigating the frequency of SIBO in IBS found that the prevalence of SIBO in subjects meeting diagnostic criteria for IBS was between 4% and 64%.[70] Variation in prevalence rates depended on the type of test used and the criteria used to define a positive test result. From the 12 studies reviewed, there was found to be a three to fivefold increase in the odds of a positive test result in individuals with IBS. However, this failed to reach statistical significance when the criteria that gave the lowest prevalence of a positive test were used.[6,11] Also, there was shown to be significant heterogeneity between studies, small study effects and publication bias leading to a likely overestimation of the prevalence of a positive test for SIBO. The authors concluded that there is insufficient evidence to justify the routine exclusion of SIBO in people with IBS. This reiterates the findings of an earlier Rome Consensus Report.[71]

In another recent systematic review and meta-analysis of case–control studies in IBS patients with abnormal breath tests, the authors came to a different conclusion – 'This meta-analysis demonstrates that the breath test is a valid and important catalyst in the development of the bacterial hypothesis for IBS'.[72] The weight of their argument (odds ratio of 9.64 for abnormal breath test in IBS vs. controls) was based on three studies that utilised age- and sex-matched controls. However, two of these studies used paediatric subjects. Also, significant between-study heterogeneity was demonstrated and there was a large imbalance between the size of case and control groups in the studies reviewed.

The continued controversy surrounding the implication of SIBO in the pathogenesis of IBS is due to a lack of confidence in the validation of breath testing.[73] It will remain a problem until robust definitions of what constitutes significant SIBO are reached. This will not happen until objective diagnostic measures are defined.