Introduction

The relationship between tissue bioburden and wound healing has been established by several studies and confirms that high bioburden delays wound healing.1,2 The reports also indicate that tissue bioburden has a greater effect on wound healing than the presence of systemic diseases, such as diabetes and cardiovascular disease. When high levels of bacteria in the wound are suspected to be the cause of nonhealing, a culture needs to be obtained. The gold standard for determining wound bacterial level is quantitative tissue biopsy, but this modality is not generally used because of potential damage to healing tissue, potential to cause pain to the patient, and the lack of expertise to process the biopsies.

The use of quantitative tissue swab culture has been suggested for determining infection in the chronic wound. Most agree that greater than 105 organisms per gram of tissue is diagnostic of infection and delayed wound healing. Bill, et al.,3 studied 38 patients with clean chronic wounds using quantitative tissue biopsies and quantitative swabs. With biopsy, 74 percent of wound samples (28) contained greater than 105 bacteria. Simultaneous quantitative swab culture of these 28 biopsies indicated infection in 22 of the 28 cases for a correlation of 79 percent. They concluded that quantitative swab culture provides a valuable adjunct for monitoring bioburden in the management of chronic wounds.

Processing quantitative swabs requires several steps, and many routine microbiology services may not want to deal with a process that complex. In contrast, the procedures for processing a semi-quantitative swab are routine in most laboratories. The only materials required are a blood agar plate, sterile loops, and an incubator. The clinical validity of using semi-quantitative swabs instead of tissue biopsies to monitor tissue levels of bacteria has been documented for burn wounds.4,5

The purpose of this study was to compare quantitative swab to semi-quantitative swab to determine the clinical acceptability of semi-quantitative swabs in identifying clean chronic wounds with greater than 105 bacteria. If proven acceptable, the use of semi-quantitative swabs to monitor bioburden in chronic wounds could be established in most wound care facilities to direct care plans.

Methodology

A nonrandomized prospective design was used to swab patients seen in a university-based wound care clinic from November, 2001, to April, 2002. All wounds were present for more than six months and included any type of cutaneous wound at any body site. No patients who had gross surface contamination, necrotic tissue, purulent drainage, or eschar were cultured. A total of 124 wounds were cultured.

Before obtaining the samples, a sterile 4cm by 4cm gauze was moistened with sterile saline, and the wound was cleaned to remove surface contamination. Next, using sterile technique, an alginate-tipped applicator (Fisherbrand, Houston, Texas) was rotated over a 1cm by 1cm area for five seconds with sufficient pressure to cause tissue fluid to be expressed. The tip of the swab was then broken off into a sterile transport tube. This swab was processed using the semi-quantitative technique. Following the acquisition of this swab sample, another swab was obtained from the same site using the same technique. The tip of this swab was broken off and placed into a sterile transport tube containing 5mL of normal saline. This swab was processed using a quantitative technique. Both samples were immediately transported to the laboratory for processing.

Serial dilutions of the quantitative swabs were performed and plated on sterile agar medium. All plated specimens were incubated under aerobic conditions at 37 degrees C. After 24 hours, the plates were visually inspected and colonies of bacteria counted. Colony-forming units (CFU) were then utilized to determine the total bacterial count on each plate.