The cause of IBS is not known; speculated mechanisms include altered GI motility, bacterial overgrowth, visceral hypersensitivity and psychological stress. Another proposed mechanism relates to the fact that up to one third of patients with IBS describe the onset of their symptoms following acute gastroenteritis. This is called post-infective IBS (PI-IBS). How acute gastroenteritis leads to persistent GI symptoms of IBS is not known. A limited amount of data suggests that patients with IBS may have an imbalance in their gastrointestinal microflora. Several studies indicate that small bowel bacterial overgrowth is more common in individuals with IBS. Symptoms of SBBO are similar to diarrhea-predominant IBS and include chronic diarrhea, bloating and abdominal pain.