Types of Spontaneous Bacterial Peritonitis
Spontaneous bacterial peritonitis (SBP) is classified into three distinct variants based on ascitic fluid analysis: classic SBP (neutrophils ≥250/mm³ with positive culture), culture-negative neutrocytic ascites (neutrophils ≥250/mm³ with negative culture), and monomicrobial non-neutrocytic bacterascites (positive culture with neutrophils <250/mm³). 1
Classic (Culture-Positive) SBP
Defined by ascitic fluid neutrophil count ≥250 cells/mm³ with positive bacterial culture showing a single organism, typically Gram-negative bacteria (especially E. coli) or Gram-positive cocci (streptococcus species and enterococci). 1
Represents the traditional presentation where both diagnostic criteria are met simultaneously. 1
Requires immediate empirical antibiotic therapy with third-generation cephalosporins plus albumin infusion. 2
Culture-Negative Neutrocytic Ascites (CNNA)
Characterized by ascitic fluid neutrophil count ≥250 cells/mm³ but negative bacterial culture despite appropriate culture techniques. 1
Accounts for approximately 40% of patients meeting neutrophil criteria for SBP, even when ascitic fluid is properly inoculated into blood culture bottles at bedside. 1
These patients demonstrate identical clinical course and outcomes to culture-positive SBP and must be treated identically with empirical antibiotics. 1
The negative culture likely reflects low bacterial concentrations in ascitic fluid or prior antibiotic exposure rather than absence of infection. 1
Monomicrobial Non-Neutrocytic Bacterascites (MNB)
Defined by positive ascitic fluid culture showing a single bacterial organism but neutrophil count <250 cells/mm³. 1
Represents either transient bacterial colonization of ascites or the early stage of developing SBP. 1
Management depends on clinical presentation: 1
- Asymptomatic patients: Often resolve spontaneously without antibiotics; repeat paracentesis is recommended, and if culture remains positive on repeat testing (regardless of neutrophil count), treatment should be initiated. 1
- Symptomatic patients: Those with fever, abdominal pain, or signs of systemic infection should receive immediate empirical antibiotics while awaiting culture results, as they may be progressing to frank SBP. 1
Important Distinctions from Secondary Bacterial Peritonitis
Secondary bacterial peritonitis (approximately 5% of cases) must be differentiated from SBP as it requires surgical intervention rather than antibiotics alone. 1
Suspect secondary peritonitis when: 1
- Multiple organisms on Gram stain or culture
- Ascitic neutrophil count >1,000/mm³
- Ascitic total protein ≥1 g/dL
- Ascitic LDH above normal serum upper limit
- Ascitic glucose ≤50 mg/dL
- Failure of neutrophil count to decrease after 48 hours of appropriate antibiotics
- Localized abdominal symptoms or signs suggesting perforation
Elevated ascitic CEA (>5 ng/mL) or alkaline phosphatase (>240 U/L) strongly suggests intestinal perforation. 1
Urgent CT imaging should be performed when secondary peritonitis is suspected. 1
Additional Variant: Spontaneous Bacterial Empyema
Spontaneous bacterial pleural empyema represents infection of pre-existing hepatic hydrothorax, diagnosed by pleural fluid neutrophils >250/mm³ with positive culture or >500/mm³ with negative culture, in the absence of pneumonia. 1
Associated with concurrent SBP in 50% of cases. 1
Pleural fluid culture in blood culture bottles yields positive results in approximately 75% of cases. 1