Wound Swab Quality Control: Diagnostic Stewardship Augments Antimicrobial Stewardship Efforts

April 15, 2021
Christina Yen, MD

Contagion, Contagion, April 2021 (Vol. 06, No. 02), Volume 06, Issue 02

Highlighted study: Marchand-Senécal X, Brasg IA, Kozak R, et al. Impact of rejection of low-quality wound swabs on antimicrobial prescribing: a controlled before-after study. Open Forum Infect Dis. 2020;8(1):ofaa609. doi:10.1093/ofid/ofaa609

Initiatives such as Choosing Wisely, which promotes avoiding unnecessary and low-value tests and procedures, recommend screening low-quality wound specimens given their negative financial and clinical impact on patientcare.1 However, little investigation has been done into the impact of wound swab quality on prescribing practices. Superficial wound swabs are widely considered to have poor diagnostic yield and their results may be difficult to interpret: are the isolates representative of contamination, colonization, or true infection?
To discern the differences, methods such as the Q score are used to determine the quality of nonsterile respiratory samples taken for culture.2-3 The score grades a sample’s quality using the quantity of neutrophils and epithelial cells; lower scores represent lower quality samples.3 A study by Marchand-Senécal et al sought to apply the Q score to nonsterile, superficial wound swabs and assess subsequent changes in lab resource utilization and antimicrobial prescribing.

The controlled before-after study was done at a 638-bed academic hospital and a 530-bed veterans’ long-term care home in Toronto, Canada.4 Applying the Q score to the quality of superficial wound swabs, those with a score of less than 1 were rejected, with an addendum to the microbiology reportstating that further processing would require a formal request by the ordering clinician. Superficial, nonduplicate wound swabs of the highest quality submitted for adult patients at the acute care or long-term care settings were included from the preintervention (March 5-September 16, 2018) and postintervention (September 17, 2018-September 16, 2019) periods. If multiple specimens of equal quality were submitted, the specimen with the largest number of different isolates was included. All low-quality specimens were part of the intervention group; high-quality swabs were part of the control group. Wound swabs from patients in outpatient clinics, operative samples, biopsies, the burn unit, or emergency department who were not admitted were excluded. The primary outcome of interest was the proportion of patients receiving antibiotics within 5 days after specimen collection. The secondary outcomes were inpatient antibiotic days of therapy (DOT) and the proportion of patients whose empiric antibiotics started on the day of swab attainment were discontinued by hospital day 5.

Of the 656 swabs included in the study, 58% (382/656) were of low quality, with 140 received in the preintervention period and 242 post intervention. Another 68% (165/242) of the postintervention, low-quality swabs were not processed. Post intervention, there were fewer antibiotic prescriptions for low-quality swabs compared with those with high-quality swab groups (4.5% vs 9.4%; 95% CI, 1.00-4.72; P=.05). Comparing pre- and postintervention low-quality swab groups, there was also an observed decrease in new prescriptions (P=.04). However, there was no change in the secondary outcomes of antimicrobial discontinuation and average DOT. Only 2 low-quality swabs were followed by physician calls for processing. Finally, more than 14,000 workload units were saved with this intervention, meaning work saved in technician time, reagents used, and cost.

This study acknowledges how the clinical microbiology lab enhances antimicrobial use interventions.5 Although it was a single-center study, and 1 of 3 that attempted to utilize the Q score on non-respiratory samples, the idea of applying diagnostic stewardship methodologies to wound swabs with observed changes in antimicrobial initiation is encouraging.6 It would be interesting to know if the 2 locations had changes to their pre-prescriptive review practices that were simply augmented by rather than wholly attributable to this intervention. Regardless, Marchand-Senécal et al have contributed a novel implementation of diagnostic stewardship that warrants further investigation into ways to enhance antimicrobial stewardship efforts nationally and globally.

Christina Yen, MD, completed her clinical infectious diseases fellowship at Beth Israel Deaconess Medical Center in Boston, Massachusetts, in June 2020. She has stayed on as the center’s infection control/hospital epidemiology fellow. Her interests are in diagnostic stewardship, antimicrobial stewardship, and hospital-acquired infections.


  1. Leis JA, Hatchette T, Ciccotelli W, et al. Choosing Wisely Canada—top five list in medical microbiology: an official position statement of the Association of Medical Microbiology and Infectious Disease (AMMI) Canada. JAMMI. 2018;3(2):61-70. doi:10.3138/jammi.2018.02.08
  2. Sharp SE. Algorithms for wound specimens. Clin Microbiol Newsl. 1999;21(14):118-120. doi:10.1016/S0196-4399(99)80011-7
  3. Bartlett RC, Tetreault J, Evers J, Officer J, Derench J. Quality assurance of gram-stained direct smears. Am J Clin Pathol. 1979;72(6):984-989. doi:10.1093/ajcp/72.6.984
  4. Marchand-Senécal X, Brasg IA, Kozak R, et al. Impact of rejection of low-quality wound swabs on antimicrobial prescribing: a controlled before-after study. Open Forum Infect Dis. 2020;13;8(1):ofaa609. doi:10.1093/ofid/ofaa609
  5. Morgan DJ, Malani P, Diekema DJ. Diagnostic stewardship-leveraging the laboratory to improve antimicrobial use. JAMA. 2017;318(7):607-608. doi:10.1001/jama.2017.8531
  6. Matkoski C, Sharp SE, Kiska DL. Evaluation of the Q score and Q234 systems for cost-effective and clinically relevant interpretation of wound cultures. J Clin Microbiol. 2006; 44(5): 1869-1872.