Assessment of Wound Bioburden Development in a Rat Acute Wound Model: Quantitative Swab Versus Tissue Biopsy
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Disclosure: Research funded by East Carolina University Research/Creative Activity Grant #99-53
Introduction
One of the greatest controversies in wound management is the debate over the usefulness of swab cultures for predicting the presence of wound infection. The swab culture method has received criticism because it is thought to only estimate wound surface microbial numbers and not intra-tissue numbers. Because of these limitations, the Centers for Disease Control (CDC) recommends the use of either wound fluid aspiration or tissue biopsy to determine the levels of bacteria in the wound bed.[1] This recommendation is also supported by the Treatment of Pressure Ulcers Guideline Panel 1994 publication.[2]
In recent years, studies have shown that quantitative swab cultures have high sensitivity (ranging from approximately 87–100%) and good specificity (85–94%) and accuracy (approximately 90–99%) (with the exception of pressure ulcers) of diagnosing wound infection when compared with either aspirated or tissue biopsy specimens.[3–9] These studies included investigations of both acute and chronic types of wounds; however, much of the research focused on chronic wounds. Based on these studies, the evidence supports the fact that a quantitative swab method of collection and culturing is an acceptable method for diagnosing wound infections in situations where aspiration and/or biopsy are not feasible or desired. This is particularly significant because a broader group of healthcare providers can utilize swabs to collect specimens and swab methods are less invasive and less painful to most patients. A recent survey indicates that approximately 54 percent of wound care specialists in the United States (US) collect only swab cultures, while approximately 42 percent collect both swab and biopsy specimens.[10] Research studies should focus now on the best type of swab/transport systems to be used, on the actual method of processing in the laboratory, and most importantly, on investigating the best method of swab collection and standardization of practices. The wound culturing survey of US wound care specialists indicates that there is great variation in the exact methods used for collection (whether clinicians cleanse or do not cleanse wounds prior to collection, the actual site within the wound that is swabbed, whether a premoistened swab or dry swab is used, the exact swab technique that is used, types of tests ordered, etc.).[10] These findings have been confirmed by two surveys conducted in the United Kingdom on select groups of wound care clinicians.[11,12]
Currently, there is no single accepted method for the performance of swab cultures. Some methods of swab collection include the 10-point diagonal and the one-point rotation methods as well as sampling a 1cm2 area of the wound bed.[13–15] To address the continuing controversy of the best culturing methods, we compared the one-point quantitative swab with a tissue culturing method in a rat acute wound model. We selected the one-point method in this model because of the relatively small size of wounds that can be induced in rats and to better avoid contamination with peri-wound flora. This method also allows tissue sampling from the same site that was swabbed. Samples were collected by each method to determine types and numbers of bacteria present in the center of the wound bed at three different times: baseline, two days post-wounding, and four or 12 days post-wounding.
Methods
Animals. Animals were maintained according to the guidelines of the Animal Care and Use in Research and Instruction of East Carolina University and the National Institutes of Health Guide for the Care and Use of Animals. Fourteen adult, female, Sprague-Dawley rats (250g) were allowed to acclimate in the animal housing facility of East Carolina University for one week prior to the experiment.
References
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