Comparison of ESwab™ Collection and WASP® Automation with Swab and Manual Plating for Smear Interpretation and Detection of Pathogens Associated with Wound Specimens

Abstract

Objectives: Current automated processing platforms are optimized using a swab collected in
liquid medium. This study assessed both gram stain and culture interpretation of wound
specimens collected by Eswab™ for gram stain and plated by the walk away automated processor (WASP®, COPAN) compared with the wound swab applied directly to a slide for gram stain and manual plating of media.

Methods: 43 wound specimens were collected in duplicate from patients attending a wound care clinic. A double Dacron swab (sponge pledgette with 1 ml Stuart medium (COPAN)) was collected first, followed by an Eswab™ (flocked swab in 1 ml of Aimes medium (COPAN)). Dacron swab specimen gram stains and plates were set up manually and interpreted according to lab protocols. Eswab™ specimens had 2 slides prepared, a cytospun prep and 30 μl pipetted onto a slide. Eswab™ tubes were subsequently loaded onto the WASP® and processed with a programmed 30 μl drop of specimen and a 4 quadrant streaking pattern. Eswab™ gram stains and plates were interpreted by different technologists blinded to each others’ results. One investigator (KC) interpreted smear correlation and plating results to final culture interpretation.

Results: Smear interpretation: Of the 43 specimens, 36 (84%), 24(67%) and 21(49%) of cytospun, 30 μl drop and direct gram stains, respectively, correlated best with final culture results. Cytospun smears were optimal in 10/36 (27.7%) due to either presence of only a single significant pathogen or in mixed specimens, allowing visualization of all organisms. Growth and isolation: Manual versus WASP® plating showed equivalent final culture results in 35(81.4%), better performance with WASP® in 6 (14%), and manual plating in 2 (4.6%). In specimens where WASP® yielded better results, specimens were either mixed allowing reporting of mixed flora, or identified a single significant pathogen. Where manual plating with direct swab was better, culture results showed only 1+ growth.

Conclusions: Eswab™ liquid collection, allowing either a cytospun or liquid gram stain provided a more concise smear interpretation correlating to the results of the final wound culture compared to swab culturette and manual smear preparation. WASP® provided consistent streaking with detection of additional true pathogens or mixed specimens in 14% of cases.

Background

Automation in the United States

  • US not currently a major user of laboratory automation
    • Changing as consolidation is occurring
  • Less likelihood of having space to handle eventual smart incubators and line systems
    • Changing as labs move off-site to new facilities
  • Microbiology mentality is not one of line equipment
    • Changing as automation benefits are realized

Lifespan Academic Medical Centers

  • 4 site Multi-hospital system 1200 beds
  • Microbiology and Molecular ID testing
    • Stat testing and blood cultures done at each site
    • Everything else sent to one site for processing
  • 50% of laboratory testing is outreach
    • Total volume is 800,000 tests/year

Evaluation of Previ-Isola and WASP® found:

✓ 54% decrease in hands on time (p< 0.0001)
✓ Specimens were better isolated with automated streaking when 2-3 organisms present in urines
✓ Planting 30ul of Eswab™ medium detected 20% additional MRSA positive screens than direct planting/VRE equivalent
✓ With Lifespan’s volume, a cost savings of approx $20,000 per year could be realized for urines alone
✓ Purchased the WASP® after assessing all prelim study data

Objective

Increased optimization of automation with addition of wound specimens

1. Would an interpretation of the gram from liquid medium/flocked swab collection be:

  • Worse, equivalent or better than traditional swab with direct swab application to slide?

2. Would tell-tale indicators of significant infection with the gram direct vs. liquid be missed?

  • E.g. Clumps of PMNs assoc. with organisms

3. Would 30 μl ESwab™ specimens yield better organism recovery than traditional swab specimens onto solid media?

4. Would 30 μl ESwab™ specimens yield better organism recovery than traditional swab specimens onto solid media?

  • Worse, equivalent, better interpretation with the culture result?
  • Would extra cost be worth the speed of making an interpretation?

Methods

  • Collected 43 duplicate specimens from patients attending a wound care clinic
  • Specimen collection was:
    • Traditional double dacron swab first (1 mL Stuart)
    • ESwab™ flocked swab second (1 mL Aimes)
    • Both placed in respective transport tube
  • Both specimens came to the central lab for processing
  • Figure 1 shows processing steps

Results

Smear Preparation

  • 36 (84%) cytospun, 24(67%) 30 μl drop and 21(49%) direct swab preparations
    • Correlated best with final culture results
  • Cytospun smears were optimal in 10/36 (27.7%) due to either:
    • Presence of only a single organism that could be visualized or
    • Mixed specimens allowing visualization of all organisms

Results Continued

Growth and Isolation

  • Manual versus WASP® plating showed equivalent final culture results in 35 (81.4%)
  • Better detection seen with WASP® in 6 (14%)
  • Better detection seen with Manual plating in 2 (4.6%)
  • In specimens where WASP® yielded better results:
    • Specimens were mixed allowing reporting of mixed flora (5) or
    • Identification of a single significant pathogen (1)
  • In specimens where Manual plating was better:
    • Culture results showed 1+ growth (SA, Mixed cutaneous)

Conclusions

  • Eswab™ liquid was superior to direct swab smear preparation
  • Cytospin> 30 μl liquid > direct
    • Cytospin prep while requiring an additional step/cytospin funnel correlated best with culture results
    • No issue on interpretation with cells was noted
  • 30 μl Eswab™ liquid media was superior to direct swab plating for growth of organisms
  • WASP® automated streaking yielded more organisms than manual streaking due to better isolation

References

ASM Poster 2012: Solutions for Implementation of the Automated PREVI Isola Plating Instrument in the Clinical Laboratory. K. C. Chapin, S.B. Andrea, M. Andrade, and L.A. Tellier
ASM Poster 2013: Cell Morphology Preservation in Specimens Collected in Eswab™ for Gram Smears

Preperation. S. Castriciano, M. Favaro, C. fontana
Poster: Comparison of Two Methods for Preparation and Reading of Gram Stains Prepared from ESwab™
Transport Media. Rachel E. Wywadis, Fran Tomashefski, and Paul P. Bourbeau

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