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