PracticeUpdate Dermatology February 2019

EDITOR’S PICKS 12

Comparing SwabWith Biopsy for Obtaining Culture Results Wound Repair and Regeneration Take-home message

COMMENT By Robert S. Kirsner MD, PhD C hronic wounds harbor bacteria and many heal despite 3 or more bacteria being present. The mere presence of bacteria in a chronic wound does not equate to a wound infection. Rather, wound infection is diagnosed by a clinician based on clinical features such as redness, warmth swelling, pain, and loss of function. Therefore, chronic wound infections are a clinical, not a microbiologic, diagnosis. However, wound cultures play a role in patient care. After a wound infection is diagnosed, clinicians should imple- ment empiric antibiotic therapy based on evidence-based algorithms or local community or hospital antibioticograms. When a patient returns in follow-up, if the infection has not improved, cul- tures help to direct further antibiotics therapy. Therefore, the findings of this article are quite important because they lend confidence to clinicians that taking a swab (as opposed to a more invasive tissue culture) is beneficial for choice of antibiotic and by helping predict which bacteria may be present deeper in the wound. As technology improves, it may still prove to be important to obtain tissue cultures for bacteria, especially if the ability to perform quantitative cultures becomes routine in a clinical setting, which currently it is not. Quantitating the amount of bacteria in tissue may aid fur- ther in helping clinicians decide if and what antibiotics are needed in the care of a patient with a chronic wound.

• This study compared samples obtained by swab and biopsy in clinical practice by including a variety of wounds and using standard sampling and culture procedures. Wound cultures from 180 patients were analyzed, and samples obtained with biopsies were compared with samples from swabs using the Levine technique. While skin flora was more frequently cultured from swabs, similar recovery rates were obtained when excluding skin flora. Swabs identified all microorganisms cultured from biopsies in 131 wounds (72.8%). • Wound swabs have been avoided with the presumption that they capture microor- ganisms from the skin surface only. When human skin flora was excluded from the comparison, 72.8% of all wounds had identical culture results in this study. Thus, swabs may be considered as an initial diagnostic tool, keeping in mind that neither biopsy nor swab can consistently identify all microorganisms present in the wound. InYoung Kim MD, PhD

Abstract The question remains whether wound swabs yield similar culture results to the traditional gold standard, biopsies. Swabs are not invasive and easy to perform. However, they are believed to capture microorganisms from the surface rather than microorganisms that have invaded tissue. Several studies compared swabs and biopsies using different populations and sampling meth- ods, complicating the ability to draw conclusions for clinical practice. This study aimed to compare swab and biopsy in clinical practice, by including a variety of wounds and using standard sam- pling and culture procedures. Swabs (Levine technique) and biopsies were taken for microbi- ological culture in a standardized manner from the same location of one wound for each patient. Statistical analyses were performed to determine overall agreement, and observed agreement and kappa for specific microorganisms. A variety of

wounds of 180 patients from different healthcare facilities in The Netherlands were included. Skin flora was more frequently cultured from swabs, resulting in similar recovery rates when excluding skin flora (1.34 vs 1.35). Swabs were able to iden- tify all microorganisms cultured from biopsies in 131 wounds (72.8%) wounds. Most frequently iden- tified organisms were Staphylococcus aureus, Pseudomonas aeruginosa, and beta-haemolytic streptococci species. Observed agreement and kappa for these organisms varied between 87.2 and 97.8% and 0.73 and 0.85, respectively. This study demonstrates that swabs and biopsies tend to yield the same culture results when taken from the same location. For frequently occurringmicro- organisms, agreement between the twomethods was even higher. Therefore, there seems to be no direct need for invasive biopsy in clinical practice.

Dr. Kirsner is Chief of Dermatology at University of Miami Hospital, and Chairman of Dermatology at the Department of Dermatology and

Cutaneous Surgery, University of Miami Miller School of Medicine in Miami, Florida.

Wound Swab and Wound Biopsy Yield Similar Culture Results. Wound Repair Regen 2018 Mar 01;26(2)192-199, M Haalboom, MHE Blokhuis- Arkes, RJ Beuk, et al. www.practiceupdate.com/c/76115

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