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World J Gastroenterol. Mar 14, 2014; 20(10): 2482-2491
Published online Mar 14, 2014. doi: 10.3748/wjg.v20.i10.2482
Irritable bowel syndrome and small intestinal bacterial overgrowth: Meaningful association or unnecessary hype
Uday C Ghoshal, Deepakshi Srivastava
Uday C Ghoshal, Deepakshi Srivastava, Department of Gastroenterology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow 226104, India
Author contributions: Ghoshal UC conceived, reviewed the data and wrote the manuscript; Srivastava D contributed to review of the data and writing of the manuscript.
Correspondence to: Uday C Ghoshal, MD, DNB, DM, FACG, RFF, Professor, Department of Gastroenterology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raebareli Road, Lucknow 226014, India. udayghoshal@gmail.com
Telephone: +91-522-249-4405 Fax: +91-522-2668017
Received: November 2, 2013
Revised: January 7, 2014
Accepted: February 17, 2014
Published online: March 14, 2014
Abstract

Irritable bowel syndrome (IBS) is a common condition characterized by abdominal pain or discomfort, bloating, and altered stool form and passage. Small intestinal bacterial overgrowth (SIBO) is a condition in which there is overgrowth of bacteria in small bowel in excess of 105 colony forming units per milliliter on culture of the upper gut aspirate. Frequency of SIBO varied from 4%-78% among patients with IBS and from 1%-40% among controls. Higher frequency in some studies might be due to fallacious criteria [post-lactulose breath-hydrogen rise 20 PPM above basal within 90 min (early-peak)]. Glucose hydrogen breath test (GHBT) has a low sensitivity to diagnose SIBO. Hence, studies based on GHBT might have under-estimated frequency of SIBO. Therefore, it is important to analyze these studies carefully to evaluate whether the reported association between IBS and SIBO is over or under-projected. This review evaluates studies on association between SIBO and IBS, discordance between different studies, their strength and weakness including methodological issues and evidence on therapeutic manipulation of gut flora on symptoms of IBS.

Keywords: Glucose hydrogen breath test, Lactulose hydrogen breath test, Functional bowel disease, Dysbiosis, Gut flora

Core tip: Irritable bowel syndrome (IBS) has been conventionally thought to be a disorder without an organic basis. However, recently data are emerging to show that it may have organic basis at least in a subset of patients. Though several studies reported an association between small intestinal bacterial overgrowth (SIBO) and IBS, the frequency of SIBO reported to vary between 4% and 78%. The current review suggests that the association between SIBO and IBS is definite, but the studies reporting high prevalence of SIBO in IBS over-estimated its frequency due to use of fallacious diagnostic methods. Better test to diagnose SIBO in patients with IBS is highly needed.