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Wound infections

Author: Vanessa Ngan, Staff Writer, 2005.

What are wound infections?

A wound infection is defined by the US Centre for Disease Control and Prevention (CDC) as surgical site infection (SSI). This is further defined as:

Although this definition of wound infection is restricted to those arising from a surgical incision, a broader and more general definition would be infection of a wound caused by physical injury of the skin as a result of penetrating trauma from plants, animals, guns, knives or other objects. Wounds break the continuity of the skin and allow organisms to gain access to tissues and cause infection.

Infections arising in surgical wounds are one of the most common hospital acquired infections and are an important cause of morbidity and mortality. Hence, the focus of this article is on the recognition and management of surgical wound infections.

What defines a surgical wound infection?

A surgical wound/site infection is defined by the following criteria:

Other signs of wound infection include:

Surgical site infections do not include stitch abscesses, episiotomy infections, newborn circumcision scars, or infected burn wounds.

What causes wound infections?

Wound infections are caused by the deposition and multiplication of microorganisms in the surgical site of a susceptible host. There are a number of ways microorganisms can get into wounds.

The most common causative organisms associated with wound infections include Staphylococcus aureus/MRSA, Streptococcus pyogenes, Enterococci and Pseudomonas aeruginosa.

Other factors that play a role in wound infection are shown in the table below.

General patient characteristics
  • Age, obesity, malnutrition
  • Endocrine and metabolic disorders
  • Smoking
  • Hypoxia, anaemia
  • Malignant disease
  • Immunosuppression
Wound characteristics
  • Nonviable tissue in wound
  • Foreign bodies
  • Tissue ischaemia
  • Haematoma formation
Operative characteristics
  • Poor surgical technique
  • Long operation time (>2 hours)
  • Intraoperative contamination
  • Prolonged preoperative stay
  • Hypothermia

What is the risk of wound infection?

The risk of wound infection varies with the type of surgery. Certain types of surgery carry a higher risk of contamination than others and have led to the following classification on surgical wounds.

ClassificationDescriptionInfective Risk (%)
Clean
  • Uninfected operative wound
  • No acute inflammation
  • No entry to internal organs
  • No break in aseptic technique
  • eg hernia repair
<2
Clean-contaminated
  • Opening to internal organ but minimal or no spillage of contents
  • No evidence of infection or major break in aseptic technique
  • eg appendectomy
<10
Contaminated
  • Opening to internal organs with inflammation or spillage of contents
  • Major break in aseptic technique
  • eg colectomy for obstruction
15-20
Dirty
  • Purulent inflammation present
  • Intraperitoneal abscess formation or visceral perforation
40

What is the management of wound infections?

The goal of wound infection management is to prevent or minimise the risk of infection. The following factors or methods external to the patient are used to prevent infection.

Techniques applied to the patient to prevent wound infections include:

Antiseptic cleansers are adequate for clean wounds or lightly contaminated wounds. Antibiotic prophylaxis may be indicated for clean-contaminated wounds and is usually recommended for contaminated wounds. Antibiotics for dirty wounds are part of the treatment because infection is already established. When deciding on a prophylactic antibiotic consider the following:

Wound infections can complicate illness, cause anxiety, increase patient discomfort and lead to death. It is estimated that surgical wound infections result in an increased length of hospital stay by about 7-10 days. Hence the prevention and management of wound infections has a major impact on both patient health and health economics.

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