About 10% of people who suffer an attack of food poisoning or gastroenteritis develop persistent symptoms of IBS. The reason for this is not clear and may be related to changes in colonic bacteria, the gut immune system and the leakiness of the gut wall as well as changes in the brain stem centres controlling the gut.  Post infectious IBS is more common in people who have suffered a more severe attack and who were also depressed, anxious and experience difficult life events at the time.