Time-related Concordance Between Swab and Biopsy Samples in the Microbiological Assessment of Burn Wounds
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Abstract: The aim of this study was to investigate the concordance between swab and tissue biopsy samples in terms of microbiological isolates and their time-related changes. A total of 156 samples (78 swab and 78 biopsy) were collected from 39 cases of partial- or full-thickness burns and compared at days 7 and 14 after admission regarding the type of microorganisms and their time-related changes. Pseudomonas aeruginosa and Citrobacter freundii were the two most common microorganisms found by both sampling methods. While the majority of swab and biopsy samples were concordant in day 7, the rate of concordance in day 14 was less than day 7—87.1% versus 66.6%, respectively. After comparing the ratio of P aeruginosa and C freundii in positive swab and biopsy cultures on days 7 and 14, unlike the swab samples, the biopsy samples yielded similar results both times (75% P aeruginosa and 25% C freundii, respectively). The results of this study show that the swab is a sufficient tool for burn wound monitoring during the first week and could defer the need for invasive biopsy sampling. For patients who remain in the burn unit for a longer period, biopsy samples are justified for monitoring the bacterial activity in burn wounds.
Address correspondence to:
Ghasemali Khorasani, MD
Mazandaran University of Medical Sciences
Emam Square, Valliasr Blvard
Sari, Mazandaran, 48157-33971
Iran
Phone: +98 151 2262342
E-mail: gakhorasani@yahoo.com
A severe burn is a serious injury that bacterial colonization often complicates. Infection impairs the healing process, and microorganism invasion of neighboring healthy tissue can lead to sepsis, which is the most frequent cause of death in burn injuries.1,2 Early detection of invasive burn wound infection could be helpful in reducing the mortality for these patients. Although tissue biopsy is considered the most appropriate sampling method for identifying wound infection and its causative pathogens,3–6 the procedure is potentially traumatic and is not routinely available, particularly for slow- or non-healing wounds that require frequent, long-term care. For these reasons, the use of a more conventional and readily available sampling method such as swab sampling could be considered as an alternative method for monitoring burn wounds. Since there are arguments to support the use of the swab sample as a useful method for routinely assessing the microbiology of appropriate wounds,7–11 we conducted this study to investigate the value of swab samples versus biopsy samples in terms of microbiological isolates and their time-related patterns of change.
Material and Methods
Setting and patients. Our burn center is a part of a 75-bed tertiary referral university-dependent hospital located in northern Iran. This prospective cross-sectional study was conducted on patients with partial- or full-thickness burns who were enrolled from September 2006 through March 2007. The Mazandaran University of Medical Sciences review board approved this study. Surface swabs and wound biopsies for bacteriological assessment of the burn wounds were performed at the end of weeks 1 and 2. Seven of the 39 patients in this study were septic based on the following clinical criteria: body temperature < 36˚C or > 39˚C, blood pressure < 90 mmHg or a reduction of 40 mmHg or more, and pulse rate > 90 beats per minute. Blood samples were taken 3 times and cultured in patients who had signs and symptoms of septicemia.
Biopsy samples. Under anesthesia, about 1 cm3 of tissue, along with the underlying live tissue, was removed from each wound and suspended in 2-mL physiological saline and homogenized. Samples were inoculated on blood and MacConkey agar.
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