Small intestinal bacterial overgrowth

Small intestinal bacterial overgrowth (SIBO), also termed bacterial overgrowth, or small bowel bacterial overgrowth syndrome (SBBOS), is a disorder of excessive bacterial growth in the small intestine. Unlike the colon (or large bowel), which is rich with bacteria, the small bowel usually has fewer than 100,000 organisms per millilitre. Patients with SIBO typically develop symptoms which may include nausea, bloating, vomiting, diarrhea, malnutrition, weight loss, and malabsorption by various mechanisms.

The diagnosis of SIBO is made by several techniques, with the gold standard being an aspirate from the jejunum that grows more than 10⁵ bacteria per millilitre. Risk factors for the development of SIBO include dysmotility; anatomical disturbances in the bowel, including fistulae, diverticula and blind loops created after surgery, and resection of the ileo-cecal valve; gastroenteritis-induced alterations to the small intestine; and the use of certain medications, including proton pump inhibitors.

SIBO is treated with an elemental diet or antibiotics, which may be given cyclically to prevent tolerance to the antibiotics, sometimes followed by prokinetic drugs to prevent recurrence if dysmotility is a suspected cause.