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

Diagnosis and Treatment of Spontaneous Bacterial Peritonitis (SBP)

Diagnostic Criteria

SBP is diagnosed when ascitic fluid polymorphonuclear (PMN) leukocyte count exceeds 250 cells/mm³, regardless of culture results. 1, 2

When to Perform Diagnostic Paracentesis

• Perform diagnostic paracentesis immediately in ALL hospitalized cirrhotic patients with ascites at admission, even without symptoms 1, 3
• Approximately 16% of SBP cases are completely asymptomatic 1
• Urgent paracentesis is mandatory in patients presenting with:
  • Fever or signs of systemic inflammation 1
  • Abdominal pain or gastrointestinal symptoms 1
  • Gastrointestinal bleeding 1, 2
  • Shock or hemodynamic instability 1
  • Hepatic encephalopathy 1
  • Worsening liver or renal function 1

Proper Specimen Collection

• Inoculate at least 10 mL of ascitic fluid into aerobic and anaerobic blood culture bottles at bedside BEFORE starting antibiotics 1, 3
• This bedside inoculation technique increases culture sensitivity to >90% 1
• Obtain blood cultures simultaneously before antibiotic initiation 1
• Culture positivity occurs in only 50-80% of cases despite proper technique 2

Diagnostic Threshold Rationale

The PMN threshold of >250 cells/mm³ is deliberately set lower than alternative thresholds (such as 500 cells/mm³) because the clinical risk of missing SBP far outweighs the risk of overdiagnosis—each hour of treatment delay increases mortality by 3.3-10% 1, 2

Culture-Negative Neutrocytic Ascites

Treat culture-negative neutrocytic ascites (PMN >250/mm³ with negative culture) identically to culture-positive SBP, as both have similar morbidity and mortality 1

Treatment Protocol

Immediate Antibiotic Therapy

Initiate empirical antibiotics immediately after diagnosis without waiting for culture results. 1, 2

First-Line Antibiotic Regimen (Community-Acquired SBP)

• Cefotaxime 2g IV every 8-12 hours for 5 days 1, 3
• This regimen achieves 77-98% resolution rates 1
• Alternative: Ceftriaxone (dosing per institutional protocol) 3
• For uncomplicated SBP in stable patients: Oral ofloxacin 400mg twice daily 1

Nosocomial or Healthcare-Associated SBP

• Use broad-spectrum antibiotics: carbapenem or piperacillin-tazobactam based on local resistance patterns 3, 4
• Do NOT use quinolones in patients already on quinolone prophylaxis, in areas with high quinolone resistance, or in nosocomial SBP 1

Treatment Duration

• 5 days of antibiotic therapy is as effective as 10 days 1

Albumin Therapy (Critical for Mortality Reduction)

Administer intravenous albumin 1.5 g/kg body weight within 6 hours of diagnosis, followed by 1.0 g/kg on day 3 1, 3

• This regimen reduces mortality from 29% to 10% 1
• Reduces type 1 hepatorenal syndrome from 30% to 10% 1
• Particularly critical in patients with creatinine ≥1.0 mg/dL or bilirubin ≥5 mg/dL 3

Monitoring Treatment Response

48-Hour Follow-Up Paracentesis

Perform repeat diagnostic paracentesis at 48 hours to assess treatment efficacy 1, 3

Treatment Success Criteria

• PMN count decreases to <25% of pre-treatment value 1, 3
• Clinical improvement accompanies laboratory response 1

Treatment Failure Definition

• PMN count fails to decrease by at least 25% from baseline 1, 3
• Worsening clinical signs and symptoms 1

Management of Treatment Failure

When treatment failure occurs at 48 hours:

• Broaden antibiotic coverage empirically or modify based on culture sensitivities 1
• Obtain CT imaging to exclude secondary bacterial peritonitis 1, 3
• Surgical consultation for possible intra-abdominal surgically treatable source 1

Distinguishing Secondary Bacterial Peritonitis

Secondary bacterial peritonitis requires different management and should be suspected when:

• Multiple organisms on Gram stain or culture (vs. monomicrobial in SBP) 2
• Ascitic PMN count often >1,000/mm³ 2
• Localized abdominal symptoms or signs 2
• Treatment failure at 48 hours 1

Secondary peritonitis requires prompt surgical consultation, broader spectrum antibiotics, and surgical treatment of underlying cause 2

Special Clinical Scenarios

Bacterascites (Positive Culture but PMN <250/mm³)

• If symptomatic: treat as SBP 1
• If asymptomatic: repeat paracentesis, as 38% will progress to frank SBP 1

Patients on Quinolone Prophylaxis

• Use cefotaxime or amoxicillin-clavulanic acid instead of quinolones 1

Prognosis

• SBP carries approximately 20% hospital mortality despite infection resolution 1, 2
• Early appropriate antibiotic treatment combined with albumin therapy significantly improves survival 1
• Delaying antibiotic therapy increases mortality by 10% for every hour's delay in cirrhotic patients with septic shock 1, 2