19th July 2023

Small Intestine Bacterial Overgrowth (SIBO)

SIBO is excessive colonisation of the small bowel with bacteria – usually coliforms, which produce gas from fermenting carbohydrates. This causes GI symptoms – most commonly abdominal bloating and pain, flatulence and diarrhoea. Risk factors include previous bowel resection or gastric bypass, connective tissue disorders (systemic sclerosis, Ehlers-Danlos, rheumatoid arthritis) and medications (narcotics and PPIs). The excessive bacteria impair the small bowel’s absorptive function, causing vitamin and nutrient deficiencies, including vitamin B12, vitamin D and iron. Folate levels, however, tend to be elevated due to its synthesis by the bacteria. The gold standard diagnostic test used to be a culture of duodenal aspirates; however, its invasive nature and expense has resulted in the most up-to-date guidelines recommending hydrogen breath testing with either glucose or lactulose as the first line investigation. SIBO can be treated with a course of broad-spectrum antibiotics – most commonly rifaximin 550mg three times daily for 14 days.