What are the most common causes of sepsis?

Most Common Causes of Sepsis

The most common causes of sepsis are Gram-negative and Gram-positive bacteria, which occur with approximately equal frequency, together accounting for more than 90% of sepsis cases. 1

Bacterial Pathogens

Gram-negative bacteria

• Common pathogens include:
  • Escherichia coli (particularly in abdominal and urinary tract infections)
  • Klebsiella species (38% of Gram-negative sepsis in low and lower-middle-income countries) 1
  • Pseudomonas species
  • Acinetobacter species (more common in Asia) 1
  • Enterobacter species

Gram-positive bacteria

• Common pathogens include:
  • Staphylococcus aureus (including MRSA)
  • Streptococcus species
  • Enterococcus species (including vancomycin-resistant strains)

Anatomical Sources of Infection

The most frequent sites of infection leading to sepsis are:

1. Respiratory tract - pneumonia is a leading cause of sepsis
2. Abdominal cavity - including intra-abdominal abscesses, peritonitis, and biliary infections
3. Bloodstream - primary bacteremia or catheter-related infections
4. Urinary tract - particularly in elderly patients and those with urinary catheters
5. Skin/soft tissue - including cellulitis, necrotizing fasciitis, and infected wounds

Other Pathogens

• Fungi - particularly Candida species, which are increasingly important causes of sepsis 1

  • Risk factors include immunosuppression, prolonged antibiotics, total parenteral nutrition, and invasive devices 1

• Viruses - less common but important in immunocompromised patients

• Parasites - rare in developed countries but important in endemic areas

Special Considerations

Patient-specific risk factors

• Healthcare-associated infections: Higher risk of resistant organisms like MRSA and vancomycin-resistant Enterococci 1
• Immunocompromised patients: At risk for atypical pathogens, including resistant Gram-negative bacilli and Candida species 1
• Neutropenic patients: Especially wide range of potential pathogens 1
• Recent antimicrobial use: Increases risk of resistant organisms 1

Regional variations

• Significant differences exist between regions:
  • Higher proportions of Acinetobacter species in Asia
  • Higher proportions of Klebsiella species in Africa 1

Changing epidemiology

• The incidence of sepsis continues to increase globally
• While historically Gram-negative bacteria were emphasized, recent studies show an increasing incidence of Gram-positive sources of sepsis 2
• Fungal causes of sepsis are increasing rapidly 3

Clinical Implications

Understanding the most likely pathogens based on patient factors and local epidemiology is crucial for appropriate empiric antimicrobial therapy. Failure to initiate appropriate therapy is associated with substantially increased morbidity and mortality 1.

When treating sepsis, empiric antimicrobial therapy should be broad enough to cover all likely pathogens, considering:

• Anatomic site of infection
• Local pathogen prevalence and resistance patterns
• Patient's immune status and comorbidities
• Recent antimicrobial exposure
• Presence of invasive devices 1

The initial empiric regimen should be narrowed once the causative pathogen is identified or clinical improvement is noted 1.