Bacterial overgrowth in irritable bowel syndrome: prevalence, diagnosis, and treatment. Review

Abstract

To date, irritable bowel syndrome (IBS) is considered as a multifactorial syndrome with the involvement of several central and peripheral pathogenic mechanisms. One of the main peripheral risk factors for IBS is the syndrome of intestinal bacterial overgrowth (SIBO). Only few studies, investigating SIBO frequency in patients with IBS, have been conducted, their nature is often incomplete and contradictory, and doesn’t consider clinical features and severity of SIBO course. The effectiveness of SIBO eradication in modifying of IBS course is unclear. The article presents an overview of current data on the prevalence of SIBO in IBS compared to controls when using various diagnostic methods, as well as the impact of SIBO eradication on the course of IBS. It is emphasized that the latest systematic reviews and meta‑analyses show that SIBO is closely related to IBS, especially IBS with diarrhea, and the prevalence of SIBO at IBS has been increasing in recent years. In addition, a positive relationship between IBS with constipation and methane‑positive SIBO is determined. The use of the H2‑lactulose breath test is the main practical method of diagnosing SIBO, although it gives significantly higher rates of its prevalence both in patients with IBS and in the corresponding healthy controls. Unfortunately, the sensitivity and specificity of SIBO diagnosis using breathing tests is limited, and the results of studies reflect significant «clinical heterogeneity» due to the lack of uniform criteria for the selection of patients and individuals of the control group. Thus, diagnostic results using hydrogen breath tests should be interpreted with caution. In view of the limitations of available diagnostic tests, there is a need to develop and validate methods to better reveal the presence of SIBO in patients with IBS and ideally guide therapy. In any case, confirmation of the presence of SIBO in patients with IBS requires the administration of antibiotics, rifaximin‑α is the most effective and safe. The clinical improvement and reduction in the frequency of relapses after eradication of SIBO indicates that the latter may play a pathogenetic role in IBS.