Is Staphylococcus aureus (S. aureus) the most common bacteria causing surgical wound infections?

Staphylococcus aureus is the Most Common Cause of Surgical Site Infections

Staphylococcus aureus is the predominant pathogen causing surgical site infections (SSIs), accounting for approximately 40-46% of all SSIs. 1 This organism leads the list of causative pathogens in most surgical wound infections, particularly in clean procedures where the gastrointestinal, gynecologic, and respiratory tracts have not been entered.

Epidemiology of Surgical Site Infections

• SSIs occur in approximately 2-5% of patients undergoing surgery in the USA 1
• Infection rates vary by surgical site and procedure type:
  • 1.5-2% for most extracavitary grafts 2
  • Up to 6% for vascular grafts in the groin 2
  • 1-5% for intracavitary grafts 2
  • Higher rates in emergency procedures and reoperations 2

Common Pathogens in Surgical Site Infections

Primary Pathogens (in order of frequency):

1. Staphylococcus aureus (39.9-45.9%) 1
2. Pseudomonas aeruginosa (10.8-12.1%) 1
3. Escherichia coli (7-9.7%) 1
4. Enterococcus species (7.7-8.2%) 1
5. Klebsiella species (5.1-5.8%) 1
6. Enterobacter species (5.6-5.8%) 1
7. Coagulase-negative staphylococci (3.4-4.2%) 1

Pathogen Distribution by Procedure Type:

• Clean procedures: S. aureus and streptococcal species predominate 2, 1
• Clean-contaminated or contaminated procedures: Aerobic and anaerobic pathogens from the normal endogenous microflora of the surgically resected organ 2
• Procedures involving axilla, GI tract, perineum, or female genital tract: Require coverage for gram-negative bacteria and anaerobes 2

Evolution of Microbial Epidemiology

The microbiology of SSIs has evolved over time:

• S. aureus was historically the predominant organism 2
• Improvements in surgical technique and prophylactic antimicrobial therapy have changed the landscape 2
• Methicillin-resistant S. aureus (MRSA) infections are increasing in frequency 2, 3
• Coagulase-negative staphylococci are now more common than S. aureus in some settings 2
• Pseudomonas aeruginosa has emerged as the most common gram-negative cause 2

Clinical Implications and Management

Diagnosis:

• SSIs rarely occur during the first 48 hours after surgery 2
• Early infections (within 48 hours) are almost always due to S. pyogenes or Clostridium species 2
• After 48 hours, SSI becomes a more common source of fever 2

Treatment:

• The most important therapy for SSI is opening the incision, evacuating infected material, and continuing dressing changes until the wound heals by secondary intention 2, 1
• Antibiotic selection should be guided by the likely pathogen:
  • For MSSA: First-generation cephalosporin or antistaphylococcal penicillin 2
  • For suspected MRSA: Vancomycin, linezolid, daptomycin, telavancin, or ceftaroline 2
  • For operations on axilla, GI tract, perineum, or female genital tract: Agents active against gram-negative bacteria and anaerobes 2

Special Considerations

• PVL-positive S. aureus strains in SSIs are associated with longer hospitalization, delayed improvement of serological markers, and increased risk of osteomyelitis 4
• Screening for nasal carriage of S. aureus and subsequent decolonization pre-operatively reduces SSIs and hospital stay, especially in major clean surgeries involving implants 5
• Staphylococcus aureus is particularly problematic in orthopedic implant infections, where it can form biofilms that protect bacteria from antibiotics 6

Surgical site infections remain a significant cause of morbidity and mortality, with S. aureus consistently identified as the leading causative pathogen across multiple studies and guidelines. Understanding this predominance helps guide empiric antibiotic therapy and infection prevention strategies.