Small Intestinal Bacterial Overgrowth

Small intestinal bacterial overgrowth (SIBO) is an excess of bacteria in the small bowel that causes gastrointestinal symptoms. It is not an invasive intestinal infection: the usual problem is carbohydrate fermentation within the lumen, producing gas, distension, altered bowel habit, and discomfort. The symptom pattern is nonspecific, so symptoms alone cannot distinguish SIBO from other gastrointestinal disorders. The clinical task is to identify the patient whose symptoms fit this mechanism and who has a reason to lose normal small-bowel protection, such as dysmotility, altered anatomy, or impaired digestive defences. Bloating alone is common in irritable bowel syndrome, dietary intolerance, constipation, and functional dyspepsia; a positive breath test should not be used to explain every gastrointestinal symptom. SIBO may recur if the underlying driver persists. Severe malabsorption and vitamin deficiency are uncommon in otherwise uncomplicated disease and increase concern for structural or surgically altered bowel.