Irritable bowel syndrome: bacteria and inflammation--clinical relevance now.

Irritable bowel syndrome (IBS) is a ubiquitous but heterogeneous syndrome characterized by abdominal pain and erratic bowel habits that affects 5% to 10% of the population. Although current definitions specify that there are no structural or biochemical abnormalities to account for the symptoms, there is growing evidence that in at least a subset of IBS patients, there is low-grade inflammation characterized by increased T lymphocytes and mast cells. Whether this is cause or effect is uncertain, as there is also clear evidence of bidirectional communication between the immune and nervous systems, and at least some of the mucosal changes could be secondary to psychological stress. A small percentage (6%-17%) of patients develop IBS symptoms for the first time after an acute episode of infective gastroenteritis (postinfective IBS), which appears to be directly responsible for low-grade immune activation. However, even in this group, preexisting psychological factors are as important as mucosal ones. Specific anti-inflammatory treatments have not been systematically evaluated, but there is no evidence of benefit currently.