Peritonitis is an inflammation of the peritoneum, a silk-like membrane covering the organs in the abdomen. Since the peritoneum lines the inner wall of the abdomen, peritonitis causes whole abdominal pain. Peritonitis is caused by bacterial or fungal infection, which can results from the complication of other medical conditions such as gastrointestinal perforation, rupture of organs, surgery. Peritonitis is a medical emergency. Please go to see you doctor right way.