Describe Surgical Site Infection in detail.

The Concept

A surgical site infection (SSI) is an infection of the operative wound, occurring within 30 days of surgery (or up to 90 days if an implant is present). It is one of the commonest healthcare-associated infections and an important cause of postoperative morbidity, so its prevention is a major focus of surgical care.

Classification & Risk

SSIs are classified by depth as superficial incisional, deep incisional, or organ/space. The risk is strongly predicted by the wound classification — clean, clean-contaminated, contaminated, or dirty (infection risk rising across these). Additional risk comes from patient factors (diabetes, obesity, smoking, immunosuppression, malnutrition) and operative factors (degree of contamination, long operating time, poor technique).

Presentation, Prevention & Management

An SSI presents with pain, erythema, swelling, warmth and purulent discharge, often with fever (typically around day 5–7). Prevention is key: appropriate antibiotic prophylaxis, aseptic technique, skin preparation, maintaining normothermia and glycaemic control, and good surgical technique. Management is to open and drain the wound, send a swab, give antibiotics if there is spreading infection, and provide appropriate dressings.

The Timing of Antibiotic Prophylaxis

A key practical detail in preventing SSI is the correct timing of antibiotic prophylaxis: a single dose is given within about 60 minutes before the skin incision, so that adequate tissue levels are present during the operation, with a repeat dose for very long procedures or major blood loss. Giving it too early or too late reduces its effectiveness. This, combined with good skin preparation, asepsis, normothermia and glycaemic control, forms an evidence-based bundle that measurably reduces surgical site infection rates.

The Bottom Line

A surgical site infection is a wound infection within 30 days (90 with an implant), its risk predicted by wound class and patient factors, prevented by prophylaxis and asepsis and treated by drainage and antibiotics.

A Note on the Wound Classes in Practice

The four wound classes translate directly into expected infection rates and prophylaxis decisions. A clean wound (e.g. A hernia repair, no viscus opened) has a very low infection rate; a clean-contaminated wound (a controlled entry into the GI/respiratory/urinary tract) a moderate rate; a contaminated wound (gross spillage, or acute inflammation) a higher rate; and a dirty wound (established infection or perforation, e.g. Faecal peritonitis) the highest. This gradation guides whether prophylactic antibiotics suffice or a full therapeutic course is needed, and whether the skin is closed primarily or left open to heal by secondary intention.

Prophylactic antibiotic within 60 minutes of incision is key.

• Surgical site infection (SSI) = wound infection within 30 days of surgery (90 days with an implant); common and important.
• Depth: superficial incisional, deep incisional, organ/space; risk predicted by wound class (clean → clean-contaminated → contaminated → dirty).
• Risk factors: diabetes, obesity, smoking, immunosuppression, malnutrition; contamination, operative duration, technique.
• Prevent: antibiotic prophylaxis, asepsis, skin prep, normothermia, glycaemic control; treat by opening/draining, swab, antibiotics, dressings.