What are the different types of spontaneous bacterial peritonitis (SBP), their definitions, and recommended management?

Types of Spontaneous Bacterial Peritonitis

Spontaneous bacterial peritonitis is classified into three distinct variants based on ascitic fluid analysis: classic SBP (neutrophils ≥250/mm³ with positive culture), culture-negative neutrocytic ascites (CNNA; neutrophils ≥250/mm³ with negative culture), and monomicrobial non-neutrocytic bacterascites (MNB; positive culture with neutrophils <250/mm³). 1

Classic Spontaneous Bacterial Peritonitis

• 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 1, 2
• Gram-positive cocci including Streptococcus species and enterococci are increasingly common pathogens 3, 4
• Requires immediate empirical antibiotic therapy without waiting for culture results 5, 6
• Culture positivity occurs in only approximately 60% of cases meeting neutrophil criteria, even with optimal technique 1

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 1
• Must be treated identically to culture-positive SBP with empirical antibiotics because clinical course and outcomes are identical 1, 3
• The negative culture likely reflects prior antibiotic exposure, low bacterial concentration, or technical limitations 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:
  • Asymptomatic patients: Often resolve spontaneously without antibiotics; perform repeat paracentesis to confirm clearance 7, 1
  • Symptomatic patients (fever, abdominal pain, signs of systemic inflammation): Require immediate empirical antibiotics 7, 1
• If repeat culture remains positive regardless of neutrophil count, the patient should be treated with antibiotics 7

Important Differential: Secondary Bacterial Peritonitis

• Must be distinguished from SBP because it requires surgical intervention rather than antibiotics alone 1
• Suspect secondary peritonitis when:
  • Multiple organisms present on Gram stain or culture 7, 1
  • Very high ascitic neutrophil count (>1,000 cells/mm³) 1, 8
  • High ascitic protein concentration (>10 g/L, often >30 g/L) 8
  • Inadequate response to appropriate antibiotic therapy 7
  • Localized abdominal symptoms or signs 7
• Elevated ascitic CEA >5 ng/mL or alkaline phosphatase >240 U/L strongly suggests intestinal perforation 5, 1
• Obtain immediate abdominal CT scan and early surgical consultation when secondary peritonitis is suspected 7

Related Condition: Spontaneous Bacterial Empyema

• Infection of pre-existing hepatic hydrothorax without pneumonia 7, 1
• Diagnosed by pleural fluid analysis showing:
  • Neutrophils >250/mm³ with positive culture, OR
  • Neutrophils >500/mm³ with negative culture 7, 1
• Pleural fluid culture in blood culture bottles yields positive results in approximately 75% of cases 7, 1
• Associated with 38% mortality and occurs in 16% of cirrhotic patients with pre-existing hydrothorax 7

Clinical Pitfalls to Avoid

• Never delay paracentesis in hospitalized cirrhotic patients with ascites—10% have SBP at admission and each hour of delay increases in-hospital mortality by 3.3% 5, 3
• Do not withhold antibiotics while awaiting culture results in patients with neutrophils ≥250/mm³—CNNA requires identical treatment to culture-positive SBP 1, 3
• Always consider secondary peritonitis in patients with inadequate clinical response, multiple organisms, or very high neutrophil counts to avoid missing a surgical emergency 7, 1