Surgical site infection: wound classes, risk factors and prevention under NICE NG125
Surgical site infection for MRCS Part A: wound classes, CDC definitions, organisms, risk factors, antibiotic prophylaxis and the NICE NG125 prevention bundle.
The CDC wound classification. The risk of infection rises from clean to dirty, and with patient and operative risk factors within each class.
Class
Definition
Examples
Clean
No inflammation; the respiratory, alimentary, genital and urinary tracts are not entered
Inguinal hernia repair, thyroidectomy, varicose vein surgery
Clean-contaminated
One of those tracts is entered under controlled conditions without unusual contamination
Elective cholecystectomy, elective bowel resection, transurethral prostate surgery
Contaminated
Fresh accidental wounds, a major break in sterile technique, gross spillage from the gut, or acute non-purulent inflammation
Appendicectomy for an inflamed, non-perforated appendix without pus; an open fracture seen early
Dirty or infected
Established infection, perforated viscus, or an old traumatic wound with devitalised tissue
Drainage of an abscess, faecal peritonitis, a neglected traumatic wound
Defining a surgical site infection
Superficial incisional
Skin and subcutaneous tissue of the incision. Purulent discharge, organisms cultured from an aseptically obtained sample, or signs of inflammation with the wound deliberately opened. A stitch abscess does not count.
Deep incisional
Fascia and muscle layers of the incision.
Organ/space
Any part of the anatomy opened or handled during the operation other than the incision, such as an intra-abdominal abscess or an infected joint.
Surveillance windows in the CDC definitions are 30 days after surgery, extended to 90 days for deep and organ/space infections after selected operations, including joint replacement. Research and audit use scoring systems such as the ASEPSIS score (Wilson, Lancet 1986) and the Southampton wound grading.
Organisms
_Staphylococcus aureus_, including MRSA, is the commonest cause after clean surgery.
Coagulase-negative staphylococci colonise implants and grow in biofilms, so infection may appear late and need removal of the implant.
Enteric Gram-negative bacilli, anaerobes such as _Bacteroides fragilis_, and enterococci follow gastrointestinal surgery.
_Streptococcus pyogenes_ and clostridia cause early, rapidly spreading infection. An infection that is florid within 24–48 hours of surgery suggests one of these, not the usual staphylococcal infection, which appears around days 5 to 10.
Risk factors
Patient: diabetes and perioperative hyperglycaemia, obesity, smoking, malnutrition, immunosuppression including corticosteroids, older age, remote infection, nasal carriage of S. aureus, and a higher ASA grade.
Operation: the wound class, a long operation, hypothermia, hypoxia, haematoma and dead space, devitalised tissue, foreign material, emergency surgery and poor technique.
The NNIS risk index (Culver, 1991) scores one point each for an ASA grade of 3 or more, a contaminated or dirty wound, and an operation longer than the 75th centile for that procedure.
Prevention: the NICE NG125 bundle
Before the operation
Showering. Advise the patient to shower or bathe with soap on the day before or the day of surgery.
Nasal decolonisation. Consider nasal mupirocin with a chlorhexidine body wash before procedures in which S. aureus is a likely cause of infection, according to local policy.
Hair removal. Do not remove hair routinely. If it must be removed, use electric clippers with a single-use head on the day of surgery, not razors, which increase infection.
Mechanical bowel preparation is not used routinely to reduce surgical site infection.
Antibiotic prophylaxis
Who. Clean surgery involving a prosthesis or implant, clean-contaminated surgery and contaminated surgery. Not routinely for clean non-prosthetic uncomplicated surgery.
When. A single intravenous dose on starting anaesthesia, or earlier if a tourniquet will be used, so that tissue levels are adequate before the tourniquet is inflated.
Repeat dosing. Give another dose if the operation lasts longer than the half-life of the antibiotic.
Dirty or infected wounds need antibiotic treatment as well as prophylaxis.
Not prolonged. WHO guidance advises against continuing prophylaxis after the operation to prevent infection.
In theatre
Hand decontamination. Before the first operation on the list, wash with an aqueous antiseptic surgical solution, using a single-use brush or pick for the nails; before later operations, use an alcoholic hand rub or an antiseptic surgical solution. Consider double gloving when glove perforation is likely and contamination would be serious.
Skin preparation. Prepare the skin immediately before incision. Alcohol-based chlorhexidine is the first choice unless it is contraindicated or the site is next to a mucous membrane, where aqueous chlorhexidine is used. If chlorhexidine is contraindicated, use alcohol-based povidone-iodine, and if both alcohol and chlorhexidine are unsuitable, aqueous povidone-iodine. Beware chemical burns from chlorhexidine in preterm babies.
Diathermy. Let alcohol-based preparations dry by evaporation and avoid pooling, because of the risk of fire. Diathermy for the skin incision is not used as a way of reducing infection.
Drapes. If an incise drape is needed, use an iodophor-impregnated one; non-iodophor incise drapes may increase infection.
Homeostasis. Keep the patient warm and maintain oxygen saturation above 95% during major surgery and recovery.
Irrigation. Do not use wound irrigation or intracavity lavage to reduce the risk of infection.
Closure. Consider triclosan-coated sutures, especially in children. After caesarean birth, consider sutures rather than staples for the skin.
After the operation
Dressings. Cover the wound with an interactive dressing at the end of the operation and change it with an aseptic non-touch technique.
Cleansing and showering. Sterile saline for cleansing up to 48 hours; patients may shower safely 48 hours after surgery; tap water after 48 hours if the wound has separated or been opened.
No topical antimicrobials for wounds healing by primary intention.
Treating infection. If cellulitis develops, give an antibiotic that covers the likely organisms, guided by local resistance patterns and microbiology. Open and drain any collection. Do not use Eusol and gauze, dextranomer or enzymatic treatments for debridement.
When infection spreads: necrotising soft-tissue infection
Necrotising fasciitis spreads along fascial planes faster than the skin changes suggest. Type I is polymicrobial, typically in diabetic or immunocompromised patients, and includes Fournier’s gangrene of the perineum and scrotum. Type II is usually group A streptococcus, sometimes with S. aureus. Clues are pain out of proportion to the signs, rapid spread, crepitus, bullae, skin necrosis and systemic toxicity.
Diagnosis is clinical. The LRINEC score (Wong, 2004) combines blood results, but a low score does not exclude the disease, and imaging must not delay surgery.
Treatment is urgent radical debridement back to bleeding, healthy tissue, broad-spectrum intravenous antibiotics including clindamycin to suppress toxin production, critical care, and a planned return to theatre within about 24 hours.
A 64-year-old man with poorly controlled type 2 diabetes develops rapidly spreading pain, crepitus and dusky discoloration of the scrotum and perineum two days after a perianal abscess was drained. He is tachycardic and hypotensive.
Which microbiological pattern is most likely to be found in the debrided tissue?
How sure are you?
Explanation
This is Fournier's gangrene, a type I (polymicrobial) necrotising fasciitis of the perineum. It typically follows anorectal or urogenital sepsis or surgery in diabetic, obese or immunocompromised patients, and cultures grow a synergistic mixture of facultative Gram-negative bacilli (such as Escherichia coli), streptococci, enterococci and anaerobes such as Bacteroides; crepitus reflects gas from anaerobic metabolism. A pure group A streptococcal growth defines type II necrotising fasciitis, usually of a limb in a previously healthy person. Clostridial myonecrosis follows deep contaminated wounds and involves muscle rather than fascia. Vibrio vulnificus causes a marine-associated monomicrobial type III infection. MRSA alone is an uncommon cause. Reference: Bailey & Love 28e.
What is the difference between a clean-contaminated and a contaminated wound?+
In a clean-contaminated operation a hollow tract (such as the bowel or biliary tree) is entered under controlled conditions without unusual contamination. A contaminated wound has gross spillage, acute non-purulent inflammation, a major break in sterile technique, or is a fresh traumatic wound.
When should antibiotic prophylaxis be given?+
As a single intravenous dose on starting anaesthesia, or earlier if a tourniquet will be used, and repeated if the operation outlasts the half-life of the antibiotic. NICE does not recommend routine prophylaxis for clean non-prosthetic uncomplicated surgery.
Which skin preparation does NICE recommend?+
An alcohol-based solution of chlorhexidine first, unless it is contraindicated or the site is next to a mucous membrane (then aqueous chlorhexidine). Povidone-iodine, alcohol-based or aqueous, is used when chlorhexidine is unsuitable.
Should hair be shaved before surgery?+
No. Hair is not removed routinely. If it has to be removed, electric clippers with a single-use head are used on the day of surgery, because razors increase the risk of infection.
When can a patient shower after surgery?+
NICE advises that patients may shower safely 48 hours after surgery.
Mangram AJ, Horan TC, Pearson ML, Silver LC, Jarvis WR. Guideline for prevention of surgical site infection, 1999. Infect Control Hosp Epidemiol 1999;20(4):250–278.
Berríos-Torres SI, Umscheid CA, Bratzler DW, et al. Centers for Disease Control and Prevention guideline for the prevention of surgical site infection, 2017. JAMA Surg 2017;152(8):784–791.
Culver DH, Horan TC, Gaynes RP, et al. Surgical wound infection rates by wound class, operative procedure, and patient risk index. Am J Med 1991;91(3B):152S–157S.
Wilson AP, Treasure T, Sturridge MF, Grüneberg RN. A scoring method (ASEPSIS) for postoperative wound infections for use in clinical trials of antibiotic prophylaxis. Lancet 1986;1(8476):311–313.
Wong CH, Khin LW, Heng KS, Tan KC, Low CO. The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections. Crit Care Med 2004;32(7):1535–1541.
Written for revision in the MRCS Part A style under our editorial standards. It is not clinical advice: always confirm against current guidance. Spotted an error? Tell us.