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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.




  • Image not available. Most intra-abdominal infections (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.

  • Image not available. Primary peritonitis generally is caused by a single organism (Staphylococcus aureus in patients undergoing continuous ambulatory peritoneal dialysis [CAPD] and Escherichia coli in patients with cirrhosis).

  • Image not available. Secondary IAIs usually are caused by a mixture of enteric gram-negative bacilli and anaerobes. This mix of organisms enhances the pathogenic potential of the bacteria.

  • Image not available. For peritonitis, early and aggressive IV fluid resuscitation and electrolyte replacement therapy are essential. A common cause of early death is hypovolemic shock caused by inadequate intravascular volume expansion and tissue perfusion.

  • Image not available. Cultures of secondary (IAI) sites generally are not useful for directing antimicrobial therapy. Treatment generally is initiated on a "presumptive" or empirical basis.

  • Image not available. Antimicrobial regimens for secondary IAIs should include coverage for enteric gram-negative bacilli and anaerobes. Antimicrobial agents that may be used for treatment of secondary IAIs include the following: (a) a carbapenem, (b) piperacillin-tazobactam, or (c) ceftazidime or cefepime plus metronidazole. An aminoglycoside or colistin may be another treatment option.

  • Image not available. Treatment of primary peritonitis for CAPD patients should include an antistaphylococcal antimicrobial such as a first-generation cephalosporin (cefazolin) or vancomycin, usually given by the intraperitoneal (IP) route.

  • Image not available. The duration of antimicrobial treatment should be for a total of 4 to 7 days for most secondary IAIs.

  • Image not available. Healthcare-associated infections are becoming more common for IAIs secondary to acute care hospital admissions or admissions from chronic care settings. The major pathogens include more resistant gram-negative flora, Candida infections causing peritonitis, and Enterococcal species.


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. ...

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