AGA Clinical Practice Update on Small Intestinal Bacterial Overgrowth: Expert Review

Gastroenterology. 2020 Jul 14;S0016-5085(20)34928-3.doi:10.1053/j.gastro.2020.06.090. Online ahead of print.

Eamonn Mm Quigley 1, Joseph A Murray 2, Mark Pimentel 3


Author information

  • 1Lynda K and David M Underwood Center for Digestive Disorders, Houston Methodist Hospital and Weill Cornell Medical College, Houston, Texas. Electronic address: equigley@houstonmethodist.org.
  • 2Division of Gastroenterology and Hepatology, Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota.
  • 3Medically Associated Science and Technology (MAST) Program, Cedars-Sinai, Los Angeles, California.


Description: Thanks to ready access to hydrogen breath testing, small intestinal bacterial overgrowth is now commonly diagnosed among individuals presenting with a variety of gastrointestinal and even non-gastrointestinal complaints and is increasingly implicated, in lay press and media in the causation of a diverse array of disorders. Its definition, however, remains controversial and true prevalence, accordingly, undefined. The purpose of this review, therefore, was to provide a historical background to the concept of SIBO, critically review current concepts of SIBO (including symptomatology, pathophysiology, clinical consequences, diagnosis and treatment), define unanswered questions and provide a road map towards their resolution.

Methods: Best Practice Advice (BPA) statements were developed following discussion by the three authors. EMMQ and MP each developed text around certain BPAs based upon a review of available literature. A complete draft was reviewed by all three authors and following discussion, re-drafting and further review and revision a final draft was agreed upon by all authors.

Best practice advice statements: The definition of SIBO as a clinical entity lacks precision and consistency; it is a term generally applied to a clinical disorder where symptoms, clinical signs and/or laboratory abnormalities are attributed to changes in the numbers of bacteria or in the composition of the bacterial population in the small intestine. Symptoms traditionally linked to SIBO include bloating, diarrhea and abdominal pain/discomfort. Steatorrhea may be seen in more severe cases. There is insufficient evidence to support the use of inflammatory markers such as fecal calprotectin to detect SIBO. Lab findings can include elevated folate and, less commonly, vitamin B12 deficiency, or other nutritional deficiencies. A major impediment to our ability to accurately define SIBO is our limited understanding of normal small intestinal microbial populations- progress in sampling technology and techniques to enumerate bacterial populations and their metabolic products should provide much needed clarity. Controversy remains concerning the role of SIBO in the pathogenesis of common functional symptoms such as those regarded as components of irritable bowel syndrome (IBS). Management should focus on the identification and correction (where possible) of underlying causes, correction of nutritional deficiencies and the administration of antibiotics. This is especially important for patients with significant maldigestion and malabsorption. While IBS has been shown to respond to therapy with a poorly absorbed antibiotic, the role of SIBO or its eradication in the genesis of this response warrants further confirmation in randomized controlled trials. There is a limited database to guide the clinician in developing antibiotic strategies for SIBO, in any context. Therapy remains, for the most part, empiric but must be ever mindful of the potential risks of long-term broad-spectrum antibiotic therapy.

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