What are the types of surgical site infections?

Types of Surgical Site Infections

Surgical site infections (SSIs) are classified into three distinct categories: superficial incisional SSI, deep incisional SSI, and organ/space SSI, each with specific characteristics and clinical implications. 1, 2

Classification of Surgical Site Infections

1. Superficial Incisional SSI

• Involves only the subcutaneous tissue between the skin and underlying muscular fascia
• Occurs within 30 days of the surgical procedure
• Diagnostic criteria includes at least one of the following:
  • Purulent drainage from the superficial incision
  • Positive culture from aseptically obtained fluid/tissue
  • Local signs of pain, tenderness, swelling, erythema after the incision is opened
  • Diagnosis made by the attending surgeon or physician 1

2. Deep Incisional SSI

• Involves deep soft tissues (fascia and muscle layers) of the incision
• Occurs within 30 days of surgery (or up to 1 year if implant is in place)
• Diagnostic criteria includes:
  • Purulent drainage from the deep incision
  • Spontaneous dehiscence or deliberate opening of the deep incision
  • Abscess or other evidence of infection found on direct examination
  • Diagnosis made by the attending surgeon or physician 1, 2

3. Organ/Space SSI

• Involves any part of the anatomy (organs or spaces) other than the incision opened during the operation
• Occurs within 30 days of surgery (or up to 1 year if implant is in place)
• Requires specific diagnosis related to the organ/space involved
• Not considered a true soft-tissue infection but rather an infection of the involved organ or space 1

Microbiology of Surgical Site Infections

The pathogens causing SSIs depend primarily on the type of surgical procedure:

• Clean procedures: Staphylococcus aureus (including MRSA) and streptococcal species are most common 1
• Clean-contaminated or contaminated procedures (involving gastrointestinal, gynecologic, or respiratory tracts): Aerobic and anaerobic pathogens from the normal endogenous microflora of the surgically resected organ 1

Common pathogens include:

• Staphylococcus aureus (39.9-45.9%)
• Pseudomonas aeruginosa (10.8-12.1%)
• Escherichia coli (7-9.7%)
• Enterococcus species (7.7-8.2%)
• Klebsiella species (5.1-5.8%)
• Enterobacter species (5.6-5.8%) 1

Clinical Presentation and Diagnosis

Signs and symptoms that differentiate the types of SSIs:

• Superficial SSI: Local signs of pain, swelling, erythema, and purulent drainage; may have minimal systemic signs 1
• Deep SSI: More extensive local signs, possible wound dehiscence, and greater likelihood of systemic signs (fever >38.5°C, tachycardia >110 beats/minute) 1, 2
• Organ/Space SSI: May present with signs specific to the organ involved, often with significant systemic signs of infection 2

Warning signs suggesting deeper infection include:

• Persistent purulent discharge despite appropriate treatment
• Dusky or macerated tissue around the incision
• Failure to respond to standard treatment for superficial SSI
• Systemic signs that persist despite antibiotics 2

Management Approach

The management differs based on the type of SSI:

Superficial Incisional SSI

• Primary treatment: Open the incision, evacuate infected material, and continue dressing changes until healing by secondary intention
• Antibiotics generally unnecessary if minimal surrounding evidence of invasive infection (<5 cm of erythema) and minimal systemic signs 1

Deep Incisional SSI

• Requires more extensive opening of the wound
• Complete evacuation of infected material
• Excisional debridement of necrotic tissue
• Antibiotics indicated, especially with systemic signs 1, 2

Organ/Space SSI

• Often requires specific drainage procedures directed at the involved organ/space
• Targeted antibiotic therapy based on culture results
• May require specialized surgical intervention 1, 2

Common Pitfalls in SSI Management

• Misdiagnosis of necrotizing infection as simple SSI
• Inadequate surgical debridement
• Overreliance on antibiotics without adequate surgical intervention
• Failure to recognize deep extension of seemingly superficial infections
• Delayed surgical consultation 2

Remember that the primary and most important therapy for any SSI is to open the incision, evacuate infected material, and continue appropriate wound care until healing occurs. Antibiotics are not a substitute for adequate surgical management but are indicated for patients with systemic signs of infection or significant surrounding cellulitis 1.