Types of Peritonitis
Peritonitis is classified into three distinct types—primary (spontaneous), secondary, and tertiary—each with different microbiology, treatment approaches, and mortality risks that directly impact patient outcomes.
Primary (Spontaneous) Peritonitis
Primary peritonitis occurs without loss of gastrointestinal tract integrity and typically presents in patients with ascites from cirrhosis 1, 2. This form:
- Involves a single organism (usually E. coli, Klebsiella, Streptococcus, or Enterococcus) 2
- Does not require surgical intervention—only antibiotic therapy 1, 3
- Is diagnosed when ascitic fluid PMN count >250 cells/mm³ 4
- Has relatively favorable outcomes with appropriate antibiotics (77-98% resolution) 3
The key distinguishing feature is the absence of an intra-abdominal source requiring surgical correction 5. Treatment consists of third-generation cephalosporins (cefotaxime 2g every 8 hours or ceftriaxone 1g every 12-24 hours) for 5-10 days 4.
Secondary Peritonitis
Secondary peritonitis results from loss of gastrointestinal tract integrity—perforation, necrosis, or trauma 2, 6. This is the most common form encountered surgically and has two subtypes:
With Free Perforation
Characterized by 1:
- PMN count usually >1,000 cells/mm³ (often thousands)
- Multiple organisms on Gram stain (frequently including fungi and enterococcus)
- At least 2 of: total protein >1 g/dL, LDH above serum upper limit, glucose <50 mg/dL
- CEA >5 ng/mL or alkaline phosphatase >240 U/L (92% sensitivity, 88% specificity for perforation) 1, 4
Without Perforation (Loculated Abscess)
- Polymicrobial infection with 2-3 aerobic and 1-2 anaerobic species 2
- Includes E. coli, B. fragilis, Pseudomonas depending on GI level 2
Critical management difference: Secondary peritonitis requires both surgical source control AND antibiotics with anaerobic coverage 1. Mortality with appropriate treatment (antibiotics + surgery) is similar to primary peritonitis treated with antibiotics alone (approximately 30-40%) 1.
Distinguishing from Primary Peritonitis
The distinction is life-saving because unnecessary laparotomy in cirrhotic patients increases mortality 4. Suspect secondary peritonitis when 4:
- PMN count >1,000/mm³
- Multiple organisms on culture/Gram stain
- Ascitic protein ≥1 g/dL
- Ascitic LDH > serum upper limit
- Ascitic glucose ≤50 mg/dL
- PMN count rises or fails to drop >25% after 48 hours of antibiotics 1, 3
If secondary peritonitis is suspected, obtain immediate CT imaging and add anaerobic coverage to third-generation cephalosporin, then proceed to laparotomy 4.
Tertiary Peritonitis
Tertiary peritonitis represents recurrent or persistent intra-abdominal infection occurring >48 hours after apparently adequate source control of secondary peritonitis 6, 7. This entity:
- Occurs predominantly in critically ill or immunocompromised patients 6
- Has the highest mortality (often >50%) among peritonitis types 7
- Features multidrug-resistant organisms including Enterococcus, Enterobacter, S. aureus, coagulase-negative staphylococci, S. epidermidis, and Candida 2, 6
- Represents an evolution/complication of secondary peritonitis rather than a truly distinct disease 6
Management requires: Broad-spectrum antibiotics covering resistant pathogens (imipenem + amikacin is referenced as standard for nosocomial/tertiary peritonitis), empiric antifungal coverage (fluconazole) until cultures return, and repeat source control procedures if surgically correctable foci exist 8.
Clinical Pitfalls
Common mistake: Treating all peritonitis in cirrhotic patients surgically. The majority have spontaneous bacterial peritonitis requiring only antibiotics—surgery dramatically increases mortality 4.
Key decision point: If a cirrhotic patient with ascites has PMN >250/mm³ but typical findings (single organism, protein <1 g/dL, normal LDH, glucose >50 mg/dL, dramatic clinical response), treat medically and avoid surgery 1. Only proceed to imaging and surgery if atypical features suggest secondary peritonitis.
Microbiologic consideration: Community-acquired secondary peritonitis favors E. coli and streptococci, while healthcare-associated/nosocomial forms favor Enterococcus, Enterobacter, and S. aureus 2. This distinction guides empiric antibiotic selection.