Causes of Peritonitis
Peritonitis is primarily classified into three types: primary, secondary, and tertiary peritonitis, with secondary peritonitis being the most common form caused by gastrointestinal perforation or infected viscera. 1
Classification of Peritonitis
1. Primary Peritonitis
- Diffuse bacterial infection without loss of integrity of the gastrointestinal tract
- No identifiable source of infection during surgical exploration
- Typically occurs in:
- Infancy and early childhood
- Cirrhotic patients with ascites
- Patients with peritoneal dialysis catheters 1
- Usually caused by a single organism:
- Escherichia coli
- Klebsiella species
- Streptococcus species
- Enterococcus species 1
2. Secondary Peritonitis
- Most common form of peritonitis (accounts for majority of cases)
- Acute peritoneal infection resulting from:
- Loss of integrity of the gastrointestinal tract
- Direct invasion from infected intra-abdominal viscera 1
- Common causes include:
- Typically polymicrobial with 2-3 aerobic and 1-2 anaerobic species 1
- Microbiology differs between community-acquired and nosocomial infections:
- Community-acquired: E. coli and streptococci more common
- Nosocomial: Enterococcus spp., Enterobacter spp., S. aureus and coagulase-negative staphylococci more common 1
3. Tertiary Peritonitis
- Recurrent infection of the peritoneal cavity following primary or secondary peritonitis
- Complication of secondary peritonitis
- Also termed "ongoing peritonitis" or "persistent peritonitis" 1
- Typically caused by multiple pathogens including:
- Previously mentioned organisms
- Staphylococcus epidermidis
- Candida species 1
- More common in critically ill or immunocompromised patients
- Often associated with multidrug-resistant organisms 1
Microbiology of Peritonitis
Common Pathogens in Secondary Peritonitis
Gram-negative bacteria (56% of isolates):
Gram-positive bacteria (29% of isolates):
- Enterococcus species (15.7%)
- Streptococcus species 1
Anaerobic bacteria (13% of isolates):
Pathophysiology
- Peritoneal infections are typically synergistic infections
- Gram-negative bacteria exert pathogenic effects through endotoxin
- Anaerobic bacteria contribute through exoenzymes and capsular polysaccharides
- Synergistic mechanisms include protection against host defense and creation of suitable environment by one member of the flora for another 5
- Adjuvant substances that worsen peritonitis include bile, gastric juice, blood, and necrotic tissue 5
Risk Factors for Peritonitis
- Post-surgical patients (especially after gastrointestinal surgery)
- Recent peritonitis
- Immunocompromised status
- Diabetes mellitus 6
- Cirrhosis with ascites (for primary peritonitis)
- Peritoneal dialysis (for primary peritonitis)
Clinical Presentation and Complications
Common symptoms: abdominal pain, tenderness, fever, nausea, and vomiting 6
Atypical presentations may occur in:
- Immunocompromised patients
- Patients with spinal cord injuries
- Patients with altered mental status
- Post-operative patients 6
Complications include:
Diagnostic Approach
- CT scan is the imaging modality of choice for adults with suspected intra-abdominal infection 6
- Ultrasonography may be useful for superficial abscesses or when CT is unavailable 6
- Intraoperative fluid (peritoneal) samples should be sent for culture and sensitivity pattern analysis 3
Treatment Considerations
- Source control is essential and includes:
- Determining the cause of peritonitis
- Draining fluid collections
- Controlling the origin of abdominal sepsis 1
- Antimicrobial therapy should cover both aerobic and anaerobic pathogens 7
- Common empiric antibiotic regimens include:
Early diagnosis and appropriate treatment of peritonitis are crucial for improving outcomes, as delayed diagnosis and treatment can significantly increase mortality 6.