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

Diagnosis of Spontaneous Bacterial Peritonitis (SBP)

SBP is diagnosed when ascitic fluid polymorphonuclear (PMN) leukocyte count exceeds 250/mm³, and diagnostic paracentesis must be performed in all hospitalized cirrhotic patients with ascites, even without symptoms of infection. 1, 2, 3

When to Perform Diagnostic Paracentesis

Perform diagnostic paracentesis immediately in the following scenarios:

• All cirrhotic patients with ascites upon hospital admission, regardless of symptoms 1, 2
• Patients with gastrointestinal bleeding 2
• Shock or hemodynamic instability 2
• Fever or signs of systemic inflammation 2
• Abdominal pain or gastrointestinal symptoms 2
• Worsening liver and/or renal function 2
• Hepatic encephalopathy 2

Critical pitfall: SBP is asymptomatic in approximately 7% of cases, making clinical criteria unreliable for diagnosis. 4 You cannot exclude SBP based on absence of symptoms—paracentesis is mandatory. 4

Diagnostic Criteria

The definitive diagnostic threshold is:

• Ascitic fluid PMN count >250/mm³ 1, 2, 3

This applies regardless of culture results. Culture-negative neutrocytic ascites (PMN ≥250/mm³ with negative culture) should be treated identically to culture-positive SBP. 3

Key characteristics of SBP:

• Typically monomicrobial infection (single organism) 3
• Most commonly gram-negative bacteria (~60%), particularly E. coli and Klebsiella pneumoniae 1
• Increasing prevalence of gram-positive organisms and multidrug-resistant organisms (MDROs), especially in nosocomial infections (35% of overall infections) 1

Proper Specimen Collection

Culture technique is critical for diagnostic yield:

• Inoculate at least 10 mL of ascitic fluid into blood culture bottles at the bedside (aerobic and anaerobic) before administering antibiotics 1, 2
• This bedside inoculation technique increases culture sensitivity to >90% 1
• Obtain simultaneous blood cultures before starting antibiotics 1, 5

Important caveat: Ascitic fluid culture is positive in only 50-80% of SBP cases, even with optimal technique. 3 Never delay treatment waiting for culture results.

Rapid Bedside Diagnosis

Leukocyte esterase reagent strips (Multistix, Combur test, Nephur-Test) can provide immediate bedside diagnosis while awaiting formal cell count:

• Sensitivity: 83-100%, Specificity: 92.5-100% 6, 7
• Positive predictive value: 75-100%, Negative predictive value: 96-100% 6, 7
• Allows immediate initiation of empirical antibiotics 6

Distinguishing SBP from Secondary Bacterial Peritonitis

Secondary bacterial peritonitis requires surgical intervention and has different characteristics:

• Localized abdominal symptoms or signs 3
• Multiple organisms on Gram stain or culture (polymicrobial) 3
• Higher ascitic PMN count (often >1,000/mm³) 3
• Requires prompt surgical consultation 3

If secondary peritonitis is suspected (e.g., diverticulitis, cholecystitis, perforation), do not treat as SBP—obtain surgical consultation and treat the underlying condition. 1

Treatment Initiation

Start empirical IV antibiotics immediately upon diagnosis (PMN >250/mm³) without waiting for culture results. 1, 2, 3

Delaying antibiotics increases mortality by 10% for every hour's delay in patients with septic shock. 2, 3

First-Line Antibiotic Therapy

For community-acquired SBP in settings without high MDRO prevalence:

• Cefotaxime 2g IV every 6-8 hours for 5 days (third-generation cephalosporin) 1, 2, 5
• Alternative: Ceftriaxone 1
• Resolution rate approximately 90% 1

For nosocomial SBP, recent hospitalization, or critically ill patients (high MDRO risk):

• Consider initial carbapenem therapy 1
• Inappropriate initial antimicrobial therapy in septic shock increases death risk 10-fold 1

Do not use quinolones if:

• Patient already on quinolone prophylaxis 2
• High quinolone resistance in your area 2
• Nosocomial SBP 2

Albumin Therapy

Administer IV albumin concurrently with antibiotics:

• 1.5 g/kg at diagnosis 2, 3, 5
• 1.0 g/kg on day 3 2, 3, 5

This significantly reduces hepatorenal syndrome risk and mortality. 2, 3, 5

Monitoring Treatment Response

Perform repeat paracentesis after 48 hours of treatment. 5

Treatment success is defined as:

• Ascitic neutrophil count decrease by at least 25% of pre-treatment value 2, 5
• Improvement in clinical signs and symptoms 2, 5

Treatment failure indicators:

• Failure of PMN count to decrease by ≥25% 2, 5
• Worsening clinical status 2, 5
• Consider resistant bacteria requiring antibiotic change or secondary bacterial peritonitis requiring surgical evaluation 5

Antibiotic Stewardship

Narrow antibiotic coverage as soon as culture results are available. 1 The emerging threat of MDROs makes stewardship critical—use broad-spectrum antibiotics for the shortest duration necessary. 1

Five-day therapy is as effective as 10-day treatment. 5

Prognosis

Despite appropriate treatment, SBP carries approximately 20% hospital mortality rate. 2, 5 However, early appropriate antibiotic treatment combined with albumin therapy significantly improves survival. 2, 5