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Source: Gross AW, Olsen KM, DiPiro JT. Intra-abdominal infections. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. Accessed April 14, 2017.


  • Intra-abdominal infection.

  • Spontaneous bacterial peritonitis.


  • Acute, inflammatory response of peritoneal lining to microorganisms, chemicals, irradiation, or foreign body injury.

    • Primary peritonitis: intra-abdominal focus may not be evident.

    • Secondary peritonitis: focal disease process evident.

    • Abscess: purulent collection of fluid separated from surrounding tissue by wall consisting of inflammatory cells and adjacent organs.

      • Usually contains necrotic debris, bacteria, and inflammatory cells.


  • Table 1 summarizes many potential causes of bacterial peritonitis.

  • Causes of intra-abdominal abscess overlap those of peritonitis.

    • May occur sequentially or simultaneously.

    • Appendicitis most frequent cause of abscess.

  • Primary peritonitis most commonly associated with end-stage alcoholic cirrhosis.

TABLE 1.Causes of Bacterial Peritonitis


  • Peritonitis.

    • Primary peritonitis.

      • Bacteria enter abdomen:

        • Via bloodstream or lymphatic system.

        • By transmigration through bowel wall.

        • Through indwelling peritoneal dialysis (PD) catheter.

        • Via fallopian tubes.

    • Secondary peritonitis.

      • Bacteria enter peritoneum or retroperitoneum as result of disruption of integrity of gastrointestinal (GI) tract caused by diseases or traumatic injuries.

      • Focal disease process.

    • Inflammatory process within peritoneum involves peritoneal lining.

      • Fluid and protein shift into abdomen (called “third spacing”)

      • May cause hypotension, hypovolemic shock, and death.

  • Abscess.

    • Forms through combined action of:

      • Inflammatory cells (eg, neutrophils)

      • Bacteria.

      • Fibrin.

      • Other inflammatory mediators.

    • Oxygen tension low within abscess, allowing anaerobic bacteria to thrive.


  • Primary peritonitis often caused by single organism.

    • Most commonly associated with end-stage alcoholic cirrhosis and with Escherichia coli

    • In children, pathogen usually group A Streptococcus, Streptococcus pneumoniae, E. coli, or Bacteroides species.

    • With PD, infection most often caused by common skin organisms: Staphylococcus epidermidis, Staphylococcus aureus, streptococci, and enterococci.

  • Secondary peritonitis most often polymicrobial (Table 2)

TABLE 2.Pathogens Isolated from Patients with Intra-abdominal Infection

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