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Wound infection.

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VOL: 101, ISSUE: 08, PAGE NO: 32

What is it?

The presence of pathogenic organisms in wounds is classified into four levels:

l Contamination - organisms do not cause any host reaction;

l Colonisation - organisms multiply or initiate a host reaction;

l Critical colonisation - organisms multiply, causing delayed wound healing and usually increased pain but no overt host reaction;

l Wound infection - deposition and multiplication of organisms in tissue with an associated host reaction.

Common infective organisms

Some wound infections are caused by fungi and protozoa, but most are caused by bacteria, in particular:

- Streptococcus pyogenes;

- Enterococcus faecalis;

- Staphylococcus aureus;

- Pseudomonas aeruginosa;

- Enterobacter species;

- Escherichia coli;

- Klebsiella species.

Causes

- Direct contact - transfer from equipment or the hands of carers.

- Airborne dispersal - micro-organisms deposited from the air.

- Self-contamination - migration from the patient’s skin or gastrointestinal tract.

Predisposing factors

- Presence of an existing chronic infection.

- Long interval between skin preparation and surgery.

- Some surgical procedures (particularly bowel).

- Major tissue loss or trauma.

- Inadequate wound drainage.

- Inappropriate use of wound management material.

- Poor aseptic technique at dressing changes.

- Necrotic tissue or slough.

- Poorly managed exudate.

Symptoms

- Erythema, pain and/or heat.

- Cellulitis.

- Oedema.

- Abscess.

- Purulent discharge

- Delayed healing.

- Discoloured tissues within and at the wound margins.

- Granulation tissue that is friable and bleeding.

- Unexpected pain and/or tenderness.

- Abnormal smell.

- Wound breakdown - when a healing wound develops strips of granulation tissue in the base instead of a uniform spread across the whole wound bed.

Diagnosis

- Confirm infection and identify the causative organism(s) and possible resistance to antibiotics.

- Swabbing is the most common sampling method used in the UK.

- Serum investigations - obtaining small amounts of blood to identify elevated white cell counts and levels of serum C-reactive protein, which is present in many acute inflammatory conditions.

- Quantitative analysis, for example through wound biopsies, can highlight an increased bacterial burden.

Treatment

- A treatment priority is to reduce the risk of cross-infection.

- Treatment should be based on holistic assessment of the patient.

- The main aim is to cut bacterial burden within the wound margins.

- Systemic antibiotics are vital to treat clinically infected wounds.

- Topical antibiotics are not indicated for infected or colonised wounds, but may be useful for acute cellulitis until a systemic antibiotic has been selected.

- In addition to antibiotics, wound-management products with silver or iodine can reduce bacterial burden.

- Other interventions that help reduce the bacterial burden include enzymatic debridement, surgical debridement, larval therapy and the use of topical negative pressure.

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