Peritonitis is inflammation of the peritoneum, usually caused by bacterial infection or chemical irritation of the peritoneum when internal organs become diseased (as with appendicitis) or when contents of the gastrointestinal tract escape (as with a perforated peptic ulcer). Characteristic pain, sometimes with shock, fever, and temporary cessation of bowel activity (ileus), are common. Urgent treatment of the cause is required, often with surgery; antibiotics may also be needed.