What are the diagnostic criteria and treatment recommendations for Spontaneous Bacterial Peritonitis (SBP)?

Diagnosis and Treatment of Spontaneous Bacterial Peritonitis (SBP)

The diagnosis of SBP is established with an ascitic fluid polymorphonuclear (PMN) leukocyte count >250/mm³, and treatment should be initiated immediately with a third-generation cephalosporin plus albumin infusion to reduce mortality. 1, 2

Diagnostic Criteria

When to Perform Diagnostic Paracentesis

• Diagnostic paracentesis should be performed in all patients with cirrhosis and ascites at hospital admission, even without symptoms suggestive of infection 1
• Additional indications for paracentesis include:
  • Gastrointestinal bleeding 1
  • Shock or hemodynamic instability 1
  • Fever or other signs of systemic inflammation 1
  • Abdominal pain or gastrointestinal symptoms 1
  • Worsening liver and/or renal function 1
  • Hepatic encephalopathy 1
  • Acute kidney injury 1

Diagnostic Confirmation

• SBP diagnosis is confirmed with an ascitic fluid PMN count >250/mm³ 1, 2
• Ascitic fluid should be cultured at bedside in aerobic and anaerobic blood culture bottles before starting antibiotics 1
• Blood cultures should also be obtained before initiating antibiotics to increase the chance of isolating the causative organism 1
• Bedside inoculation of at least 10 mL of ascitic fluid into blood culture bottles increases culture sensitivity to >90% 1

Special Diagnostic Considerations

• Bacterascites: PMN count <250/mm³ with positive ascitic fluid culture 1
  • If patient has signs of systemic inflammation, treat with antibiotics 1
  • If asymptomatic, perform repeat paracentesis when culture results return positive 1
• Spontaneous bacterial pleural empyema: Consider in patients with pleural effusion 1
  • Diagnosis based on pleural fluid with positive culture and PMN >250/mm³ OR negative culture with PMN >500/mm³ 1
• Secondary bacterial peritonitis: Must be differentiated from SBP 1
  • Suspect with localized abdominal symptoms, multiple organisms on culture, very high PMN count, or inadequate response to therapy 1
  • CT scanning is recommended for suspected secondary bacterial peritonitis 1

Treatment Recommendations

Empirical Antibiotic Therapy

• Initiate empirical antibiotics immediately after diagnosis, without waiting for culture results 1, 2
• First-line treatment: Third-generation cephalosporins 1, 2
  • Cefotaxime 2g IV every 8 hours for 5 days is recommended 1, 2
  • A 5-day therapy is as effective as a 10-day treatment 1, 2
• Alternative options:
  • Amoxicillin/clavulanic acid (initially IV, then oral) 1
  • Ciprofloxacin (initially IV, then oral) 1
• Avoid potentially nephrotoxic antibiotics (e.g., aminoglycosides) 1

Albumin Therapy

• Intravenous albumin should be administered at 1.5 g/kg at diagnosis and 1 g/kg on day 3 2
• Albumin significantly reduces the risk of hepatorenal syndrome and mortality 2

Monitoring Response

• Perform repeat paracentesis after 48 hours of treatment 2
• Treatment failure is defined as:
  • Failure of ascitic neutrophil count to decrease by at least 25% of pre-treatment value 2
  • Worsening of clinical signs and symptoms 2
• If treatment fails, consider:
  • Resistant bacteria requiring antibiotic change based on culture results 2
  • Secondary bacterial peritonitis requiring surgical evaluation 2

Evolving Microbiology Patterns

• Traditionally, gram-negative bacteria (especially E. coli and Klebsiella) were most common (60%) 1, 3
• Recent shift toward gram-positive bacteria and multidrug-resistant organisms (MDROs), particularly in nosocomial and healthcare-associated SBP 1, 4
• MDROs represent approximately 35% of infections in cirrhotic patients 1
• This shift has led to decreased response to standard empirical antibiotics 1

Prognosis

• SBP has approximately 20% hospital mortality rate despite infection resolution 2
• Early appropriate antibiotic treatment combined with albumin therapy significantly improves survival 2

Common Pitfalls and Caveats

• Delaying antibiotic therapy increases mortality - in cirrhotic patients with septic shock, mortality increases by 10% for every hour's delay in initiating antibiotics 1
• Up to one-third of patients with SBP may be entirely asymptomatic or present with only encephalopathy and/or acute kidney injury 1, 5
• Ascitic fluid culture is frequently negative even when performed in blood culture bottles, but is important for guiding antibiotic therapy 1, 6
• Consider secondary bacterial peritonitis in patients with inadequate response to therapy or polymicrobial cultures 1, 5