Post-Infectious IBS Post-Infectious IBS (PI-IBS) Irritable Bowel Syndrome (IBS) is classified as a functional gastrointestinal disorder , meaning it affects how the digestive system functions rather than causing obvious structural damage. In people with IBS, the bowels become more sensitive and the intestinal muscles contract differently than normal. This can lead to abdominal discomfort, bloating, and changes in bowel habits . One lesser-known type of IBS is post-infectious