AndyGI infections are pretty common and can be viruses or bacteria, some are spread person to person, some are from things that grow in food (aka food poisoning).Most of the time the infecting organism is destroyed by the immune system in short order and is gone. However, there are some parasites (like Giardia) that can set up residence for along period of time.The problem is not the organism, the problem is the friendly fire. In the war against invaders our bodies produce all sorts of evil nasty and vicious chemicals. Sometimes these things damage us as well as getting rid of the organism. It takes awhile for the damage to heal, and in some cases it may never heal. Inflamation in the GI tract has been shown to depopulate the nerves in the ganglia in the gut wall (in rats with chemical inflamation). It is quite common for people who do not have IBS and do not develop IBS to have GI problems for a few weeks after clearing an infection. This is while the body is healing from the friendly fire. Sometimes the damage is too great and in the wrong place and a functional disorder occurs (IBS is one of a series of GI related functional disorders) some percentage of people recover eventually, some have IBS for the rest of their lives.HTHK.