Surgical site infections

SSI Basics - The Unwanted Souvenir

• Infection occurring at or near a surgical incision within 30 days of the procedure, or within 90 days if prosthetic material is implanted.
• Top Pathogens: Staphylococcus aureus (most common), coagulase-negative staphylococci, Enterococcus spp., and E. coli.
• Classification by Depth:
  • Superficial Incisional (skin, subcutaneous tissue)
  • Deep Incisional (fascia, muscle)
  • Organ/Space

⭐ Most SSIs become clinically apparent between postoperative day 5 and 10.

Causative Organisms - The Usual Suspects

• Staphylococcus aureus: The most frequent cause (~30%), typically originating from the patient's skin or nasal flora.
• Other Gram-Positives:
  • Coagulase-negative staphylococci (e.g., S. epidermidis), common in procedures involving prosthetic implants.
  • Enterococcus spp., often seen after abdominal or pelvic surgeries.
• Gram-Negatives:
  • Escherichia coli, Klebsiella spp., and Enterobacter spp. are common after GI/GU surgeries.
  • Pseudomonas aeruginosa.
• Anaerobes:
  • Bacteroides fragilis is a key pathogen in colorectal surgery.

⭐ In clean surgeries (e.g., cardiac, neuro), skin flora like S. aureus and S. epidermidis are the predominant pathogens. In contrast, contaminated surgeries (e.g., bowel resection) have a higher incidence of polymicrobial infections with Gram-negative rods and anaerobes.

Risk & Prevention - Dodging the Infection

• Patient Risk Factors:

  • Smoking, obesity (BMI > 30), malnutrition
  • Comorbidities: Diabetes (HbA1c > 7%)
  • Nasal carriage of S. aureus

• Procedural Risk Factors:

  • Emergency surgery, prolonged duration
  • Contaminated wound class
  • Improper skin prep, intra-op hypothermia

• Core Prevention Steps:

  • Pre-op: Antiseptic shower, glucose control <180 mg/dL
  • Intra-op: Hair clipping (no razors), chlorhexidine prep, maintain normothermia

⭐ Most SSIs are caused by Staphylococcus aureus, originating from the patient's own skin flora. This makes pre-operative screening and decolonization a key preventive strategy in high-risk surgeries like cardiac or orthopedic procedures.

Diagnosis & Management - The Aftermath Plan

• Diagnosis: Primarily clinical (erythema, pain, purulent drainage).

  • Obtain deep wound cultures before starting antibiotics.
  • Imaging (CT/ultrasound) to detect deeper collections/abscesses.

• Management:

  • Source Control: Open the wound, explore, debride necrotic tissue, and drain purulent material. Leave wound open to heal by secondary intention.
  • Antibiotics: Empiric therapy targeting common pathogens (S. aureus, streptococci), then tailor based on culture results.

⭐ Most SSIs manifest 5-7 days post-op. Early onset (<48 hrs) suggests Group A Strep or Clostridium perfringens.

High‑Yield Points - ⚡ Biggest Takeaways

• S. aureus is the most common cause of SSIs; consider MRSA.
• SSIs typically appear within 30 days of surgery, or up to 1 year with prosthetic material.
• Prophylaxis with Cefazolin (1st-gen cephalosporin) is standard, given <60 minutes before incision.
• Colorectal surgery requires anaerobic coverage (e.g., cefoxitin, metronidazole).
• Major risk factors include diabetes, obesity, smoking, and prolonged surgery.
• Diagnosis is clinical: erythema, warmth, pain, and purulent drainage.
• Treatment involves incision and drainage plus systemic antibiotics.