What is the difference between spontaneous, secondary, and tertiary bacterial peritonitis?

Differences Between Spontaneous, Secondary, and Tertiary Bacterial Peritonitis

Spontaneous bacterial peritonitis (SBP), secondary bacterial peritonitis, and tertiary bacterial peritonitis are distinct clinical entities with different pathophysiology, microbiology, and management approaches, requiring prompt recognition for optimal outcomes.

Spontaneous Bacterial Peritonitis (SBP)

• Primary peritonitis (also known as spontaneous bacterial peritonitis) is a diffuse bacterial infection without loss of integrity of the gastrointestinal tract, typically seen in cirrhotic patients with ascites or in patients with a peritoneal dialysis catheter 1
• SBP has a low incidence on surgical wards and is usually managed without surgical intervention 1
• Typically monomicrobial (caused by a single organism) 1, 2
• Most commonly caused by gram-negative aerobic bacteria, with E. coli being the predominant pathogen (32-67% of culture-positive cases) 2, 3
• Other common causative organisms include Klebsiella species, Streptococcus species, and Enterococcus species 2, 3
• Diagnosis is made when polymorphonuclear leukocyte count in ascitic fluid is >250/mm³ 1
• Treatment involves empirical antibiotic therapy, typically third-generation cephalosporins like cefotaxime or ceftriaxone 1, 3

Secondary Bacterial Peritonitis

• Secondary peritonitis is the most common form of peritonitis and occurs when the peritoneal space is contaminated by endogenous microflora secondary to loss of integrity of the gastrointestinal tract 1
• Typically polymicrobial - in most clinical settings, two to three aerobic species and one to two anaerobic species are identified 1
• Common organisms include E. coli, Klebsiella spp., Streptococcus spp., Enterococcus spp., B. fragilis, and Pseudomonas spp. 1
• Requires both source control (surgical intervention) and antibiotic therapy 1
• Can be distinguished from SBP by several criteria (Runyon's criteria):
  • PMN count >1,000/mm³ 1
  • Multiple organisms on Gram stain or culture 1, 4
  • Ascitic total protein concentration ≥1 g/dL 1, 4
  • LDH level above the normal upper limit of serum LDH 1
  • Ascitic glucose concentration ≤50 mg/dL 1, 4
  • Elevated levels of ascitic fluid CEA (>5 ng/mL) or alkaline phosphatase (>240 U/L) 1
• Mortality is significantly higher than in SBP (66.6% vs. 26.4%) 4

Tertiary Bacterial Peritonitis

• Tertiary peritonitis is a recurrent infection of the peritoneal cavity that occurs >48 hours after apparently successful and adequate surgical source control of secondary peritonitis 1
• More common among critically ill or immunocompromised patients 1
• Often associated with multidrug-resistant organisms (MDROs) 1
• Typically caused by multiple pathogens, including all organisms found in secondary peritonitis plus Staphylococcus epidermidis and Candida species 1
• Associated with high morbidity and mortality 1
• Some experts suggest the terms "ongoing peritonitis" or "persistent peritonitis" may better indicate that it represents secondary peritonitis lasting longer and harboring other (selected and more resistant) pathogens 1

Key Differences in Microbiology

• SBP: Usually monomicrobial, predominantly gram-negative aerobic bacteria (E. coli) 1, 2
• Secondary peritonitis: Polymicrobial with both aerobic and anaerobic species 1
• Tertiary peritonitis: Multiple pathogens including resistant organisms, Staphylococcus epidermidis, and Candida species 1

Key Differences in Management

• SBP: Primarily managed with antibiotics without surgical intervention 1
• Secondary peritonitis: Requires both source control (surgery) and antibiotic therapy 1
• Tertiary peritonitis: Requires broader antimicrobial coverage for resistant organisms, possibly antifungals, and potentially additional surgical interventions 1

Clinical Pearls and Pitfalls

• Always suspect secondary peritonitis when multiple organisms are isolated from ascitic fluid 5, 4
• Persistence of signs and symptoms of peritonitis despite improvement in ascitic fluid analysis should prompt evaluation for secondary peritonitis 6
• Imaging (particularly abdominal CT) is crucial for diagnosing secondary peritonitis 1, 4
• Delay in surgical intervention for secondary peritonitis is associated with increased mortality 4
• The differentiation between spontaneous and secondary bacterial peritonitis is crucial for proper management and outcomes 5, 7