Peritonitis is inflammation of the serous lining of the peritoneal cavity. This inflammation may result from a response to microorganisms and/or chemical irritants, such as blood, bile, and pancreatic secretions. The peritoneal cavity is lubricated with 20 to 50 mL of clear yellow transudative fluid, normally with fewer than 300 cells/mm3 (consisting of mainly mononuclear cells), a specific gravity below 1.016, and protein (consisting of mainly albumin) below 3 g/dL.

In this chapter infectious causes of peritonitis are considered. Two major types of infective peritonitis exist: (1) primary (spontaneous or idiopathic) and (2) secondary. When signs of peritonitis and sepsis persist after treatment for secondary peritonitis and no pathogens or usually only low-grade pathogens are isolated, the clinical entity has been termed tertiary peritonitis. Intraperitoneal abscesses can result from (1) localization of the initially diffuse peritoneal inflammatory response to one or more dependent sites (ie, the pelvis, the right or left subphrenic spaces, which are separated by the falciform ligament, and Morrison's pouch, which is the most posterior superior portion of the subhepatic space and is the lowest part of the paravertebral groove when the patient is recumbent) or (2) at the site of the intra-abdominal source of the infection (eg, periappendiceal, pericholecystic, or peridiverticular abscess). Peritonitis may also result from the use of a peritoneal catheter for dialysis or central nervous system ventriculoperitoneal shunting. For management of peritoneal catheter-related peritonitis, see Chapter 94, Dialysis-Related Infection.