What are the causes of peritonitis?

Causes of Peritonitis

Peritonitis is classified into three distinct types based on etiology: primary (spontaneous), secondary (most common), and tertiary (recurrent), each with different causative mechanisms and clinical implications. 1

Primary Peritonitis (Spontaneous Bacterial Peritonitis)

Primary peritonitis occurs as a diffuse bacterial infection without any breach in gastrointestinal tract integrity and is characteristically monomicrobial. 1, 2, 3

High-Risk Populations

• Cirrhotic patients with ascites are the most common population affected 1, 2
• Patients on peritoneal dialysis with indwelling catheters 2
• Children in infancy and early childhood 1

Causative Organisms

• E. coli is the predominant pathogen, accounting for 32-67% of culture-positive cases 1, 2
• Klebsiella species are the second most common 1, 2
• Streptococcus species (including Streptococcus pneumoniae) 1, 2
• Enterococcus species 1
• These three organisms together account for nearly three-fourths of all primary peritonitis cases 2

Pathophysiology

• Bacterial translocation from the gut to mesenteric lymph nodes 4
• Depressed reticuloendothelial phagocytic system activity 4
• Decreased antimicrobial capacity of ascitic fluid 4

Secondary Peritonitis

Secondary peritonitis is the most common form of peritonitis and results from loss of gastrointestinal tract integrity, causing peritoneal contamination with endogenous microflora. 1, 3

Gastrointestinal Perforation Causes

• Duodenal perforation (peptic ulcer disease) - most common in many series (26.2%) 5
• Typhoid ileal perforation (24.2% in endemic areas) 5
• Ruptured appendix/gangrenous appendicitis (16.8%) 1, 5
• Small bowel perforation (jejunal and ileal) - increasingly common cause 6
• Diverticular perforation 1
• Gastric perforation 5, 6

Postoperative Causes

• Anastomotic dehiscence is a common cause of secondary peritonitis in the postoperative period 1

Other Visceral Causes

• Infected intra-abdominal viscera without frank perforation (e.g., gangrenous appendicitis, gangrenous cholecystitis) 1
• Ischemic bowel 1
• Traumatic perforations 1

Microbiology

• Secondary peritonitis is characteristically polymicrobial, typically involving 2-3 aerobic species and 1-2 anaerobic species 1, 2
• Common aerobic/facultative organisms: E. coli, Klebsiella spp., Enterobacter spp., Enterococcus spp., Streptococcus spp. 1
• Common anaerobic organisms: Bacteroides fragilis group, Clostridium species, Peptostreptococcus species 1, 7, 8
• Pseudomonas aeruginosa may be present depending on the level of gastrointestinal disruption 1

Community-Acquired vs. Nosocomial Differences

• Community-acquired peritonitis: E. coli and streptococci predominate 1
• Nosocomial peritonitis: Enterococcus spp., Enterobacter spp., S. aureus, and coagulase-negative staphylococci are more common 1

Tertiary Peritonitis

Tertiary peritonitis is a recurrent or persistent infection of the peritoneal cavity that follows inadequately treated primary or secondary peritonitis. 1, 3

Characteristics

• Also termed "ongoing peritonitis" or "persistent peritonitis" 1
• Represents a complication of secondary peritonitis 1, 3

Causative Organisms

• Multiple pathogens, often multidrug-resistant organisms 3, 9
• All organisms from secondary peritonitis plus:
  • Staphylococcus epidermidis 1
  • Candida species 1
  • Quinolone-resistant organisms in patients with prior prophylaxis 9, 4

Special Considerations

Tuberculosis

• Tuberculous peritonitis presents with lymphocytic-predominant ascites and should be considered in endemic areas, HIV/AIDS patients, or those on immunosuppressive therapy 10
• Adenosine deaminase (ADA) levels >32-40 U/L have 100% sensitivity and 96.6-100% specificity 10

Malignancy-Related

• Malignancy-related ascites also presents with lymphocytic ascites 10
• Elevated CEA levels are highly specific for malignancy 10

Clinical Pitfall

• When multiple organisms are isolated from ascitic fluid, always consider secondary bacterial peritonitis (due to intestinal perforation) rather than primary peritonitis 2
• Low ascitic fluid glucose (<50 mg/dL) and multiple organisms suggest secondary rather than primary peritonitis 2, 3