Dear Editor:
We agree with Dr. Zamierowski that our study that compared semiquantitative swab cultures to quantitative tissue and swab cultures would have been strengthened had the order in which the swab specimens were obtained been randomized. In retrospect, we should have discussed this issue as a limitation of the study findings. By not randomizing the order of swab acquisition, bias may have been introduced into the study findings. As suggested by Dr. Zamierowski, this bias may have resulted in fewer microbes being collected by the second swab, the semiquantitative swab, because the amount of “tissue juice” collected by this specimen may have been less than the amount of wound fluid collected by the first swab, the quantitative swab culture.
Although we have no data to support that each specimen collected an equal amount of wound fluid, we did assure that wound fluid was obtained on each swab during data collection procedures by observing the height of fluid “wicking” on the swab. During this process it appeared that we were able to obtain a comparable amount of fluid on both swabs. If in fact comparable amounts were not collected on each swab, then the potential bias would call into question our conclusions based on direct comparisons of the semiquantitative and quantitative swab cultures (ie, the third study question). However, we disagree with Dr. Zamierowski’s assertion that this study only addresses the “difference between first and second swabs,” because the swabs were processed using different laboratory procedures, which may account for some of the differences found.
In addition, we disagree that none of the study questions can be addressed because the swabs were not collected in a random order. The first and second study questions directly compared the semiquantitative swab results to the quantitative tissue results. Tissue specimens were collected over the same 1-cm2 area as the semiquantitative specimens immediately following the semiquantitative specimen. The same 1-cm2 area was used for both swab and tissue specimen collection to avoid the variability in organism recovery that may have been introduced from different sampling locations. Given the comparable conditions with respect to time, order, and location, conclusions based on comparisons between the semiquantitative and tissue cultures are not confounded by order of acquisition of the two swab specimens.
As Dr. Zamierowski stated, quantitative cultures are not available to many clinicians despite the fact that quantitative swab cultures may be more accurate (when compared to tissue cultures) than semiquantitative swabs (when compared to tissue cultures). Therefore, clinicians continue to rely on semiquantitative and qualitative swab cultures to guide treatment decisions. Perhaps the more salient practice issue is identification of those dimensions of wound culture data (qualitative, quantitative, or both) that are related to wound outcomes. Although this study compared swab cultures to quantitative tissue cultures, there remains substantial controversy over the role of microbial load in the pathogenesis of chronic wounds.
Sue E. Gardner, PhD, RN
The University of Iowa College of Nursing and the
Center for Research in the Implementation of Innovative Strategies, Iowa City Veteran's Affairs Medical Center, Iowa City, Iowa
Rita A. Frantz, PhD, RN
The University of Iowa College of Nursing,
Iowa City, Iowa
Stephen L. Hillis, PhD
Center for Research in the Implementation of Innovative Strategies, Iowa City Veteran's Affairs Medical Center, Iowa City, Iowa
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