Surgical Site Infection

Introduction

A surgical site infection (SSI) is an infection occurring at or near a surgical incision, developing within 30 days of the operation, or within a year if prosthetic material (mesh, a joint replacement, a cardiac device) was implanted. It is one of the commonest hospital-acquired infections and a significant driver of prolonged admission, readmission, reoperation and cost, which is why so much of surgical practice is built around measures to prevent it rather than simply treat it once it occurs.

Classification

The standard classification, based on CDC/NHSN criteria, describes how deep the infection extends - a distinction that changes both severity and management.¹

Surgical wound classification and risk

Every operation is assigned a wound class at the time of surgery, which predicts baseline infection risk and is one of the factors guiding whether and how antibiotic prophylaxis is given.

Risk factors

Patient factors

• Diabetes mellitus, particularly with poor perioperative glycaemic control
• Obesity
• Smoking
• Malnutrition
• Immunosuppression
• Older age and a higher ASA grade
• An existing infection elsewhere in the body at the time of surgery

Operative factors

• Longer duration of surgery
• Higher wound class, as above
• Emergency rather than elective surgery
• Perioperative hypothermia
• Poor perioperative glycaemic control
• Inadequate timing or choice of antibiotic prophylaxis

Prevention

Prevention runs across the whole perioperative pathway, and each stage has its own specific, evidence-based measures.²

Preoperative

• Treat any existing infection before elective surgery wherever possible
• Optimise diabetic control ahead of elective procedures
• Encourage smoking cessation
• Hair removal only if it will interfere with the operation, using clippers rather than a razor, and performed immediately before surgery rather than the night before - razors cause microabrasions that increase infection risk
• Preoperative skin washing with soap
• MRSA screening and decolonisation ahead of relevant procedures

Antibiotic prophylaxis

A single IV dose given within 60 minutes before incision is the standard for most clean-contaminated, contaminated and higher-risk clean procedures (agents needing a longer infusion, such as vancomycin, are started earlier, around 120 minutes before incision, to ensure adequate tissue levels at the time of the first cut). The choice of agent depends on the procedure and its likely flora - for example cefuroxime with metronidazole for GI surgery, or a single cephalosporin for clean orthopaedic or cardiac procedures - guided by local protocols.

Intraoperative

• Active warming to maintain normothermia - hypothermia impairs immune function and wound healing and independently increases SSI risk
• Good perioperative glycaemic control, avoiding both hyperglycaemia and hypoglycaemia
• Chlorhexidine-alcohol skin antisepsis, now generally preferred over povidone-iodine based on the evidence for lower SSI rates
• Strict sterile technique, minimising theatre traffic and door opening, and appropriate use of laminar airflow for implant/prosthetic procedures
• Adequate haemostasis and gentle tissue handling to reduce devitalised tissue

Postoperative

• Leave an uncomplicated surgical dressing undisturbed for the first 24-48 hours, which is when the wound is most vulnerable to external contamination
• Use an aseptic non-touch technique for any dressing change
• Continue good glycaemic control into the postoperative period
• Avoid unnecessary continuation of antibiotics beyond the prophylactic window described above

Clinical features and diagnosis

• Superficial incisional SSI - localised erythema, warmth, tenderness and purulent discharge from the incision
• Deep incisional SSI - deeper pain, fever, and sometimes wound dehiscence or a deep collection found on exploration or imaging
• Organ/space SSI - features specific to the site involved, for example fever and abdominal pain with an intra-abdominal collection after bowel surgery

Ultrasound or CT is used where an organ/space infection is suspected - for example, a suspected intra-abdominal collection - both to confirm the diagnosis and to guide percutaneous drainage where appropriate.

Management

• Superficial SSI - often managed by opening and draining the wound and allowing healing by secondary intention, with oral antibiotics added only if there is surrounding cellulitis or systemic upset
• Deep incisional or organ/space SSI - usually needs surgical debridement or drainage (open or radiologically guided) of any collection, alongside IV antibiotics directed by deep tissue or fluid culture; source control is as essential here as in any other deep-seated infection
• Necrotising surgical site infection - rare, but a surgical emergency managed exactly as necrotising fasciitis, with urgent debridement rather than antibiotics alone

Complications

• Wound dehiscence, and in severe cases evisceration
• Incisional hernia
• Prolonged hospital stay and readmission
• Sepsis
• Chronic sinus formation, particularly with retained mesh or other implanted material, sometimes requiring its removal
• Significant cosmetic and psychological impact
• Increased mortality associated with the underlying infection

Red flags

Prognosis

Most superficial SSIs resolve well with wound care and, where needed, a short course of oral antibiotics. Deep incisional and organ/space infections carry substantially more morbidity, often needing further intervention and a longer recovery. At a population level, SSI meaningfully increases length of stay, readmission rates and healthcare costs, and is independently associated with increased mortality - which is why the prevention measures above, though individually modest, are applied so consistently across every operating theatre.