Gerontological Nursing Interventions Research Center (GNIRC)

Title: Diagnostic Validity of Semi-quantitative Swab Cultures
Principal Investigator : Sue E. Gardner, PhD, RN
Study Site: University of Iowa

Abstract
Currently, there exists no noninvasive, validated method for monitoring the infection status of chronic wounds most common among older adults. The purpose of this pilot study is to obtain preliminary evidence of the diagnostic validity of semi-quantitative swab cultures obtained using Levine's technique to identify localized chronic wound infection. The specific aims of this pilot are to:

•  Identify which semi-quantitative swab culture value (i.e., 1+, 2+, 3+ or 4+) is most valid for identifying localized chronic wound infection.

•  Compare the performance of semi-quantitative swab cultures with quantitative swab cultures.

This pilot will employ an observational, cross-sectional design and the sample will include newly enrolled subjects in a Department of Veteran's Affairs (VA) Nursing Research Initiative study (NRI-01-005-1). Subjects are enrolled who have full-thickness, non-arterial chronic wounds. Enrollment will include 25 subjects.

The primary study variables are 1) quantitative swab cultures obtained using Levine's technique, 2) semi-quantitative swab cultures obtained using Levine's technique , and 3) quantitative cultures of wound tissue specimens (gold standard). Quantification of swab specimens will be expressed as number of colony forming units (CFU) per swab. Specific to this pilot, the second swab specimen obtained using Levine's technique will be semi-quantitatively processed and expressed as 1+, 2+, 3+, or 4+. Quantification of tissue specimens will be as number of CFU per gram of tissue. Wound infection will be defined as 1,000,000 organisms per gram of tissue or the presence of beta hemolytic streptococci .

The sensitivity, specificity, predictive value, and accuracy of semi-quantitative swab cultures will be calculated based on the 'true' infection status (i.e., quantitative tissue culture findings). The criteria to interpret semi-quantitative cultures as positive or negative (e.g., 3+ or 4+) will be evaluated by plotting a receiver operating characteristic (ROC) curve which will identify the optimum cut-value for sensitivity and specificity. To address the second aim, the ROC curve for semi-quantitative and quantitative swab cultures will be plotted and the area under the curves compared.

Examining the diagnostic validity of the semi-quantitative swab culture would provide evidence for ultimately developing a best practice guideline for diagnosis of wound infection in practice settings where quantitative processes are unavailable. This knowledge will significantly improve the care of older persons who have a high prevalence of chronic wounds and are often in settings where quantitative laboratory processes are inaccessible.