What is the difference between Spontaneous Bacterial Peritonitis (SBP) and bacterial peritonitis in terms of diagnosis and treatment?

Difference Between Spontaneous Bacterial Peritonitis (SBP) and Bacterial Peritonitis

Spontaneous bacterial peritonitis (SBP) is defined as a bacterial infection of ascitic fluid without any intra-abdominal surgically treatable source of infection, while secondary bacterial peritonitis results from perforation or inflammation of an intra-abdominal organ requiring surgical intervention. 1

Diagnostic Differences

Spontaneous Bacterial Peritonitis (SBP)

• Diagnosis is based on an ascitic fluid polymorphonuclear (PMN) leukocyte count >250/mm³, regardless of culture results 1, 2
• Typically monomicrobial infection (single organism) 1
• Ascitic fluid culture is positive in only about 50-80% of cases (higher with bedside inoculation into blood culture bottles) 1, 3
• No evidence of surgically treatable intra-abdominal source of infection 1
• Common in patients with cirrhosis and ascites (prevalence: 1.5-3.5% in outpatients, 10% in hospitalized patients) 1

Secondary Bacterial Peritonitis

• Often presents with localized abdominal symptoms or signs 1
• Multiple organisms typically seen on Gram stain or in culture 1
• Higher ascitic PMN count (often >1,000/mm³) 1
• Higher ascitic total protein concentration (≥1 g/dL) 1
• Elevated LDH in ascitic fluid (above normal upper limit of serum LDH) 1
• Lower ascitic glucose concentration (≤50 mg/dL) 1
• Elevated ascitic fluid CEA (>5 ng/mL) or alkaline phosphatase (>240 U/L) may indicate intestinal perforation 1
• Requires imaging (CT scan) for diagnosis and surgical evaluation 1

Treatment Differences

Spontaneous Bacterial Peritonitis (SBP)

• Immediate empirical antibiotic therapy upon diagnosis 2
• First-line treatment: third-generation cephalosporins (e.g., cefotaxime 2g IV every 6-8 hours for 5 days) 2, 4
• Intravenous albumin (1.5 g/kg at diagnosis and 1 g/kg on day 3) significantly reduces risk of hepatorenal syndrome and mortality 2
• No surgical intervention required 1
• Treatment success defined as decrease in ascitic neutrophil count by at least 25% of pre-treatment value with clinical improvement 2
• Prophylactic antibiotics recommended after first episode to prevent recurrence 4

Secondary Bacterial Peritonitis

• Requires prompt surgical consultation and intervention 1
• Broader spectrum antibiotics often needed to cover multiple organisms 1
• Mortality rate is higher (50-80%) compared to SBP (approximately 20%) 1, 2
• Surgical treatment of the underlying cause (e.g., perforation, abscess) is essential 1
• Imaging-guided drainage may be required in addition to antibiotics 1

Clinical Presentation Differences

Spontaneous Bacterial Peritonitis (SBP)

• Often subtle or asymptomatic presentation 3
• May present with fever, abdominal pain, altered mental status, or worsening of liver function 1, 3
• Signs of systemic inflammation: hyper/hypothermia, chills, altered white blood cell count, tachycardia, tachypnea 1
• Worsening of hepatic encephalopathy, renal function, or GI bleeding may be the only manifestation 1

Secondary Bacterial Peritonitis

• More likely to present with localized abdominal pain and tenderness 1
• Often has more pronounced signs of peritoneal irritation 1
• May have signs specific to the underlying cause (e.g., signs of bowel perforation) 1
• Inadequate response to standard antibiotic therapy for SBP 1

Common Pitfalls and Caveats

• Delaying antibiotic therapy in suspected SBP increases mortality by approximately 10% for every hour's delay in patients with septic shock 2
• Unnecessary laparotomy in cirrhotic patients with SBP misdiagnosed as secondary peritonitis increases mortality 1
• Culture-negative neutrocytic ascites (PMN count ≥250/mm³ but negative culture) should be treated as SBP 1
• Bacterascites (positive culture but PMN count <250/mm³) requires treatment only if the patient is symptomatic or has signs of infection 1
• Patients with cirrhosis and ascites should undergo diagnostic paracentesis at hospital admission to rule out SBP, even without symptoms suggestive of infection 1, 2
• Multidrug-resistant organisms are increasingly common in SBP, particularly in healthcare-associated and nosocomial infections, which may require alternative antibiotic strategies 3, 5