WOUND INVESTIGATIONS
Wound investigations should generally only be undertaken in wounds that are not healing and display signs and symptoms of infection or for the presence of multi-resistant bacteria such as MRSA (Gilchrist, 2000).
Tissue biopsy
The acquisition of a tissue biopsy following initial debridement and cleansing of superficial debris is recognised as being the most useful method for determining the microbial load and the presence of invasive pathogens. A tissue biopsy enables both the identification of the organism(s) present in the wound and the virulence. However, this method is restricted in day-to-day practice as it can be costly, potentially cause more tissue damage, may be traumatic to the patient and requires a skilled practitioner.
(Bowler et al., 2001; IWII, 2022).
Wound fluid sampling
In wounds where there is a large amount of exudate present, the exudate from the deeper pockets can be aspirated by needle using an aseptic technique.
The method may not be as accurate as tissue sampling, though it is less traumatic to the patient but still provides reliable results (Bowler et al., 2001; IWII, 2022).
Wound swabbing
This is the simplest and frequently used method of wound sampling and involves the use of a cotton-tipped swab to sample superficial wound fluid and tissue debris. It has been questioned whether a wound swab provides accurate results about the microorganisms, as this may only provide information about colonising bacteria and not about the bacteria invading host tissues (Patel, 2010).
Although the value of acquiring superficial swab samples has been seriously questioned, the procedure is simple, inexpensive, non-invasive and convenient for the majority of wounds (Bowler et al., 2001). However, there is often a delay in obtaining results, during which time the patient’s condition could deteriorate if not treated (EWMA, 2006; Dow, 2008). It is recognised that the Levine technique is a more effective and preferrable swabbing technique than the Z-swab method. (WUWHS, 2022)
Levine technique
A swab is rotated over a 1cm2 area of the wound with sufficient pressure to express fluid from within the wound tissue (WUWHS, 2008; IWII, 2022).
Bowler et al., (2001) stress the importance of providing accurate and relevant information to microbiology in order to facilitate appropriate wound investigation.
An important factor to consider when sampling a wound for microorganisms is the administration and route of antimicrobial therapy. If a patient is receiving treatment, microbial isolation from swab samples is likely to be significantly influenced by topical antimicrobial agents (particularly in chronic, ischaemic wounds), whereas the micro-flora of deep tissue is more likely to be influenced by systemic antibiotic therapy. Other information should include the type and site of the wound and whether the wound appears infected. Microbiology results can vary depending on the quality of the swab taken and the information provided on the specimen request form (Parker, 2000).