Wound infections

Definition of wound infection

1992 US Centre for Disease Control
Defined the following:
- Surgical site infections
- Superficial incisional infection
- Deep incisional infections
- Organ space infections

Surgical site infections must fulfill the following criteria
- Infection must occur within 30 days of surgery
- Infection must involve only the skin and subcutaneous tissue
- There must be at least one of the following
  - Purulent discharge from a superficial infection
  - Organisms isolated from aseptically obtained wound culture
- Must be at least one of the following signs of infection
  - Pain or tenderness
  - Localised swelling
  - Redness or heat

Predisposing factors

General factors
- Age, obesity, malnutrition
- Endocrine and metabolic disorders
- Hypoxia, anaemia
- Malignant disease
- Immunosupression
Local factors
- Necrotic tissue
- Foreign bodies
- Tissue ischaemia
- Haematoma formation
- Poor surgical technique
Microbiological contamination
- Type and virulence of organism
- Size of bacteriological dose
- Antibiotic resistance

Aerobic pathogens in wound infections

Staphylococcus aureus (17%)
Enterococci (13%)
Coagulase-negative staphylococci (12%)
Escherichia coli (10%)
Pseudomonas aeruginosa (8%)
Enterobacter species (8%)
Proteus mirabilis (4%)
Klebsiella pneumoniae (3%)
Candida species (2%)

Prevention of wound infection

Exogenous
- Sterilisation of instruments, sutures etc
- Positive pressure ventilation of operating theatres
- Laminar air flow in high risk areas
- Exclusion of staff with infections
Endogenous
- Skin preparation
- Mechanical bowel preparation
- Antibiotic prophylaxis
- Good surgical technique

Wound infection rates

Risk of wound infection varies with type of surgery
Infection rate can be reduced with antibiotic prophylaxis

Clean surgery

No viscus opened (e.g. hernia repair)
Infection rate typically 1-2%

Clean-contaminated

Viscus opened but no spillage of gut contents (e.g. right hemicolectomy)
Infection rate usually <10%

Contaminated

Viscus opened with inflammation or spillage of contents (e.g. colectomy for obstruction)
Infection rate 15-20%

Dirty

Intraperitoneal abscess formation or visceral perforation
Infection rate 40%

Antibiotic prophylaxis

Prophylaxis is the use of antibiotics to prevent infection
Treatment is their use to eradicate established sepsis.
Prophylaxis important in:
- Surgery with a high incidence of post-operative infection (e.g. colonic surgery)
- Surgery where infection would be hazardous (e.g. prosthetic valves)
Need to consider:
- The use of an appropriate antibiotic based on likely bacteria and tissue penetration
  - Cefuroxime & metronidazole for colonic surgery
  - Benzylpenicillin for peripheral vascular surgery
- Timing and duration of administration
  - Intravenous administration at induction
  - Number of doses - usually no more than three doses

Bibliography

Horan T C, Gaynes R P, Martone W J, Jarvis W R, Emon T G. CDC definitions of nosocomial surgical site infections, 1992: a modification of CDC definitions of surgical wound infections. Am J Infect Control 1992; 20: 271-274.

McDonald M, Grabsch E, Marshall C, Forbes A. Single-versus multiple-dose antimicrobial prophylaxis for major surgery: a systematic review. Aust N Z J Surg 1998; 68: 388-396.