SN1 SHORT NOTE 5M ★ High-yield

Describe surgical site infection with its classification, prevention and management.

Microbiology · 2nd Professional — Para-Clinical

Definition and Classification

A surgical site infection (SSI) is an infection occurring at or near the surgical incision within 30 days of the operation, or within 90 days where an implant has been placed.

Type	Extent
Superficial incisional	Skin and subcutaneous tissue only
Deep incisional	Fascia and muscle layers
Organ / space	Any part opened or manipulated during the operation — for example an intra-abdominal abscess or mediastinitis. The most serious

Wound class	Description	Expected infection rate
Clean	Elective, no inflammation, and the respiratory, gastrointestinal and genitourinary tracts not entered — hernia repair, thyroidectomy	Under 2%
Clean-contaminated	A hollow viscus entered under controlled conditions without significant spillage — elective cholecystectomy, hysterectomy	About 5 to 10%
Contaminated	Major break in technique, gross spillage, acute non-purulent inflammation, or a fresh traumatic wound	About 15 to 20%
Dirty / infected	Established infection, perforated viscus, or an old traumatic wound with devitalised tissue	Over 30 to 40%

Organisms — Staphylococcus aureus (including MRSA) is much the commonest overall, with coagulase-negative staphylococci in implant surgery; gram-negative bacilli and anaerobes after gastrointestinal and gynaecological surgery, reflecting the flora of the organ opened
The source is usually the patient's own skin or gut flora, not the theatre environment — which determines where prevention should be directed

CLINICAL PEARL

Antibiotic prophylaxis given after the incision is worthless, and given for days afterwards is harmful. The purpose is a bactericidal tissue concentration at the moment contamination occurs — so the dose goes in within 60 minutes before incision, is repeated during long operations or major blood loss, and stops within 24 hours. Continuing it "until the drain comes out" prevents nothing, selects resistant flora and increases C. Difficile risk.

Prevention

Phase	Measures
Pre-operative	Treat remote infection and optimise nutrition and glycaemic control; stop smoking for at least 4 weeks; shorten pre-operative stay; bathe with soap or chlorhexidine; and DO not shave — if hair must be removed use clippers immediately before surgery, since a razor causes microabrasions that measurably increase infection
Antibiotic prophylaxis	A single dose of an appropriate agent within 60 minutes before incision; re-dose in prolonged surgery; discontinue within 24 hours
Intra-operative	Surgical hand preparation; skin antisepsis with alcoholic chlorhexidine (superior to aqueous povidone-iodine); sterile drapes, gowns and gloves; meticulous technique with gentle tissue handling, haemostasis and avoidance of dead space; normothermia; maintained tissue oxygenation; minimising theatre traffic and door opening; and validated sterilisation of instruments
Post-operative	Aseptic dressing technique; hand hygiene; keep the incision covered for 24 to 48 hours; maintain glycaemic control; remove drains early; and post-discharge surveillance

Diagnosis, Treatment and Applied Aspects

Diagnosis is clinical — pain, erythema, swelling, warmth, purulent discharge, wound dehiscence and fever, usually appearing between the fifth and tenth post-operative days
Very early infection (within 48 hours) suggests Streptococcus pyogenes or Clostridium perfringens, both of which are aggressive and require immediate action
Send pus or tissue, not a superficial swab — a swab of the wound surface grows colonising flora, whereas deep pus or tissue identifies the true pathogen
The primary treatment is drainage — opening the wound, removing sutures where needed, debriding necrotic tissue, and dressings; antibiotics are adjunctive, and are indicated for cellulitis, systemic features, an implant or deep involvement. Antibiotics alone will not treat a collection
Do not shave the site, and if hair removal is needed use clippers just before surgery; shaving the night before is traditional in many Indian hospitals and measurably increases infection
Give prophylaxis on time and stop it on time; both errors are common, and prolonged surgical prophylaxis is one of the largest sources of unnecessary antibiotic use in Indian hospitals
Control the blood glucose perioperatively even in non-diabetics, since hyperglycaemia impairs neutrophil function and is an independent risk factor
Follow the patient after discharge; most surgical site infections appear after the patient has gone home, so a rate calculated from inpatient data alone is a substantial underestimate

All questions in Hospital Infection & Infection Control

Every Microbiology chapter →