Ten top tips for taking a wound swab
25/05/10 | Assessment and diagnosis, Infection | Rose Cooper
In this practical guide, Rose Cooper offers tips for when and how to take a wound swab, using an established technique.
Methods of obtaining a specimen from a wound include wound swabbing, needle aspiration and wound tissue biopsy. Although wound swabbing is the most practical and widely used, it is important to use a technique that produces reliable samples for microbiological analysis. In this practical guide, Rose Cooper offers tips for when and how to take a wound swab, using an established technique.
WHEN TO TAKE A WOUND SWAB
The technique usually employed for transferring clinical samples from wounds to microbiology laboratories is the wound swab; however definitive guidelines for this relatively simple procedure have yet to be established. Uncertainty about when swabs should be taken, the correct collection procedure and the appropriate protocols for submitting swabs for investigation have led to a situation where clinicians regularly collect and process unsuitable samples.
Wound infection is normally diagnosed on clinical criteria (classical signs and symptoms, as well as odour and increased exudate), rather than bacteriological criteria, as wounds may be colonised by microbial species without any adverse effect on healing. Therefore routine microbiological investigation is not justified [1,2].
However, laboratory investigation does provide clinicians with information about the organisms present in a wound and their antibiotic sensitivities, which can inform decisions about future management strategies.
Swabs should therefore be collected only when clinical criteria point to a wound infection and before any antimicrobial interventions have been initiated.
HOW TO TAKE A WOUND SWAB
It should be noted that the best technique for swabbing wounds has not been identified and validated. The following recommendations can be used as a guide and should be used in conjunction with local protocols:
1. When a swab is indicated, the patient should be given a concise explanation of the need for microbiological investigation and what the procedure involves, for example, that swabs are mainly used to recover species from the surface layers rather than from the deep tissues of a wound.
2. Before a representative sample is collected, any contaminating materials such as slough, necrotic tissue, dried exudate and dressing residue should be removed by cleansing the wound with tap water, sterile saline or debridement.
3. Sterile swabs with cotton or rayon tips are usually used. If the wound is moist a swab can be used straight from the packaging - if the wound is dry, then the swab tip should be moistened with sterile saline to increase the chances of recovering organisms from the site [Fig 1]. Swabs with a transport medium that incorporates charcoal enhance the survival of fastidious organisms .
Fig 1 – Moistening the swab tip with saline
4. Care should be taken to ensure that the swab only comes into contact with the wound surface.