In gastroenterology, irritable bowel syndrome (IBS) or spastic colon is a functional bowel disorder characterized by abdominal pain and changes in bowel habits which are not associated with any abnormalities seen on routine clinical testing. It is fairly common and makes up 20--50% of visits to gastroenterologists. Lower abdominal pain, and bloating associated with alteration of bowel habits and abdominal discomfort relieved with defecation are the most frequent symptoms. The abdominal pain type is usually described in a patient as either diarrhea-predominant, constipation-predominant or IBS with alternating stool pattern. In some individuals, IBS may have an acute onset and develop after an infectious illness characterised by two or more of the following: fever, vomiting, acute diarrhea, or positive stool culture. This post-infective syndrome has consequently been termed "post-infectious IBS" and is acute onset. This condition is more homogeneous, being mostly ddiarrhea predominant and is drawing much clinical investigation.