Spontaneous Bacterial Peritonitis

Basics

Infection of ascitic fluid without an evident intra-abdominal surgically treatable source:
- Ascitic fluid polymorphonuclear leukocyte count (PMN) >250/mL with a positive bacterial peritoneal fluid culture
Must be distinguished from secondary bacterial peritonitis (from an intra-abdominal visceral infection):
- Nonsurgical management of secondary bacterial peritonitis carries 100% mortality
- Surgical management of spontaneous bacterial peritonitis (SBP) carries 80% mortality
Up to 30% yearly incidence of SBP in patients with ascites

Mechanism:
- Portal hypertension causes translocation of intestinal bacteria through edematous gut mucosa to the peritoneal cavity
- Variceal bleeding increases the risk of SBP due to a compromised barrier between the gastrointestinal (GI) tract and blood stream
- Transient bacteremia with low serum complement
- Decreased host defense mechanisms
- Impaired activity of reticuloendothelial system phagocytosis and opsonization
- Can also seed ascitic fluid via bacteremia from extra-abdominal infections
Usually seen in the setting of cirrhosis:
- Rare in other conditions causing ascites (e.g., nephrotic syndrome, CHF)
Predominant organisms:
- 63% aerobic gram-negative (Escherichia coli, Klebsiella, others)
- 15% gram-positive (Streptococci/Staphylococci)
- 6–10% enterococci
- <1% anaerobic
Gram-positives account for 50% of cases in patients who are on prophylactic therapy with fluoroquinolones

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