Key Facts

SSI is a significant cause of post-operative morbidity, prolonged hospital stay, increased cost, and mortality. Prevention through best practice ('care bundles') is more effective than treatment.

Epidemiology

~3-5% of all surgical procedures; higher in emergency surgery (~10%). Accounts for ~16% of all healthcare-associated infections in UK. Increases hospital stay by ~7-10 days. Estimated cost: ~£10,000 per SSI episode.

Aetiology

Patient factors: Obesity, diabetes, smoking, malnutrition, immunosuppression, extremes of age, chronic disease Surgical factors: Wound classification, surgical duration, technique, emergency surgery, foreign body/implant, drains, hypothermia, hyperglycaemia Microbial factors: MRSA carriage, pre-existing infection, wound contamination

Pathophysiology

• Bacterial contamination of surgical wound → exceeds host defence capacity → infection

• 10⁵ organisms per gram of tissue generally required for infection (lower threshold with foreign body/implant)

• Biofilm formation on implants → chronic infection resistant to antibiotics

Superficial SSI (Most Common)

• Within 30 days of surgery
• Involves skin and subcutaneous tissue only
• Erythema, warmth, swelling, tenderness around wound
• Purulent discharge
• Wound dehiscence may occur

Deep SSI

• Involves fascia and/or muscle layers
• May present with deep wound abscess
• Fever, pain, systemic sepsis possible

Organ/Space SSI

• Infection in any part of the body opened/manipulated during surgery (excluding the incision)
• e.g., Intra-abdominal abscess after laparotomy, empyema after thoracotomy
• May present days-weeks post-operatively with fever, pain, or sepsis

Red Flags

• Systemic sepsis (fever, tachycardia, hypotension) with wound signs
• Rapidly spreading wound infection — consider necrotising fasciitis
• Prosthetic joint infection — orthopaedic emergency
• Sternal wound infection post-cardiac surgery — high mortality

Bedside

• Wound assessment: Signs of infection (rubor, calor, tumor, dolor, pus)
• Wound swab: If purulent discharge — send for MC&S (not routine for surveillance)
• Observations: NEWS2

Bloods

• FBC, CRP: Raised WCC and CRP
• Blood cultures: If systemic sepsis
• Procalcitonin: May help guide antibiotic duration

Imaging

• USS: Wound collection/abscess
• CT: Deep/organ-space SSI (e.g., intra-abdominal abscess)
• MRI: Prosthetic joint infection, osteomyelitis

Prevention (NICE NG125 — SSI Care Bundle)

• Pre-operative: MRSA screening and decolonisation, smoking cessation, glucose optimisation, nutritional optimisation, hair removal with clippers (not razor), skin preparation (2% chlorhexidine in 70% isopropyl alcohol)
• Intraoperative: Prophylactic antibiotics at induction (within 60 minutes before incision), maintain normothermia (>36°C), meticulous surgical technique, minimise tissue handling
• Post-operative: Sterile dressing for 48 hours, hand hygiene, appropriate wound care

Prophylactic Antibiotics

• Clean surgery without implant: Not routinely indicated
• Clean with implant: Single dose at induction (e.g., cefazolin 2g IV)
• Clean-contaminated: Single dose at induction (e.g., co-amoxiclav 1.2g IV)
• Contaminated/dirty: Therapeutic course of antibiotics (not just prophylaxis)

Treatment of Established SSI

• Superficial: Open wound, drain pus, irrigate; may not need systemic antibiotics if localised
• Deep/organ-space: IV antibiotics (guided by cultures); drainage of collections (percutaneous or surgical)
• Implant-related infection: Often requires implant removal, debridement, prolonged antibiotics
• MRSA SSI: Vancomycin 15-20mg/kg IV BD or linezolid 600mg IV/PO BD

Referral Criteria

• Deep/organ-space SSI — surgical team
• Prosthetic joint infection — orthopaedic specialist
• MRSA infection — microbiology advice

• Superficial SSI: Usually resolves with local wound care; minimal morbidity
• Deep/organ-space SSI: Significant morbidity; may require reoperation; mortality ~5-10% in severe cases
• Prosthetic joint infection: Complex; may require implant removal; long-term functional impact
• Increased hospital stay: ~7-10 days per SSI episode
• Financial cost: ~£10,000 per SSI episode
• Prevention: Care bundles reduce SSI rates by 30-50%

Wound Classification (CDC)