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Upon completion of the chapter, the reader will be able to:

  1. Define and differentiate between primary and secondary intra-abdominal infections (IAIs).

  2. Describe the microbiology typically seen with primary and secondary IAIs.

  3. Describe the clinical presentation typically seen with primary and secondary IAIs.

  4. Describe the role of culture and susceptibility information for diagnosis and treatment of IAIs.

  5. Recommend the most appropriate drug and nondrug measures to treat IAIs.

  6. Recommend an appropriate antimicrobial regimen for treatment of a primary and a secondary IAIs.

  7. Describe the patient-assessment process during the treatment of IAIs.


Intra-abdominal infections (IAIs) are those contained within the peritoneal cavity or retroperitoneal space. The peritoneal cavity extends from the undersurface of the diaphragm to the floor of the pelvis and contains the stomach, small bowel, large bowel, liver, gallbladder, and spleen. The duodenum, pancreas, kidneys, adrenal glands, great vessels (aorta and vena cava), and most mesenteric vascular structures reside in the retroperitoneum. IAIs may be generalized or localized. They may be contained within visceral structures, such as the liver, gallbladder, spleen, pancreas, kidney, or female reproductive organs. Two general types of IAI are discussed throughout this chapter: peritonitis and abscess. (Peritonitis is defined as the acute inflammatory response of the peritoneal lining to microorganisms, chemicals, irradiation, or foreign-body injury.)

An abscess is a purulent collection of fluid separated from surrounding tissue by a wall consisting of inflammatory cells and adjacent organs. It usually contains necrotic debris, bacteria, and inflammatory cells. Peritonitis and abscess differ considerably in presentation and approach to treatment.


Peritonitis may be classified as primary, secondary, or tertiary. Primary peritonitis, also called spontaneous bacterial peritonitis, is an infection of the peritoneal cavity without an evident source of bacteria from the abdomen.1,2 In secondary peritonitis, a focal disease process is evident within the abdomen. Secondary peritonitis may involve perforation of the gastrointestinal (GI) tract (possibly because of ulceration, ischemia, or obstruction), postoperative peritonitis, or posttraumatic peritonitis (eg, blunt or penetrating trauma). Tertiary peritonitis occurs in critically ill patients, and it is an infection that persists or recurs at least 48 hours after apparently adequate management of primary or secondary peritonitis.

KEY CONCEPT Most IAIs are secondary infections that are caused by a defect in the GI tract that must be treated by surgical drainage, resection, and/or repair. Primary peritonitis develops in 10% to 30% of hospitalized patients with alcoholic cirrhosis.3 Patients undergoing continuous ambulatory peritoneal dialysis (CAPD) average one episode of peritonitis every 2 years.4 Secondary peritonitis may be caused by perforation of a peptic ulcer; traumatic perforation of the stomach, small or large bowel, uterus, or urinary bladder; appendicitis; pancreatitis; diverticulitis; bowel infarction; inflammatory bowel disease; cholecystitis; operative ...

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