Performance of Eswab® Collection System Comparing to Semi-solid Swab in Gram Smear and Culture Interpretation and Reporting in Clinical Microbiology Laboratory

Abstract

Background

Few studies have assessed the impact of Eswab® on Gram smear, culture interpretation and reporting from clinical specimens. We evaluated the performance of Eswab collected specimens planted by WASP® inoculator (EW) and by manual method (EM), comparing to the results obtained by conventional planting using semi-solid swab collection kit (CP).

Method

Protocol A: A total of 200 clinical specimens were collected on semi-solid swabs and planted routinely. These samples were then transferred by sterile technique into the Eswab vials and planted manually and by WASP for Gram smear (where applicable) and culture. Protocol B: Nasal and buccal specimens were collected from 10 volunteers in Eswab and semi-solid swabs. Additional 20 clinical bronchoscopic wash and drainage fluid specimens were transferred into Eswab vials and the semi-solid swabs. Gram smear and culture were performed by the three methods. The results of EW or EM were compared to that of CP and categorized based on the impact on working up and reporting as Agreement (A), minor discrepancy (MinD), and major discrepancy (MD).

Results

1) Smear interpretation: Protocol A: For WBC quantitation, 40% of specimens had MinD and 11% had MD, while 51% showed MinD and 4% MD for bacterial quantitation between EW and CP. Changes in cell morphology was noted in 12.5% of Eswab Gram smears where cells appeared more dense, difficult to differentiate between WBC and RBC, and contained more debris and background staining than the conventional swabs. Protocol B: 25% of the samples had MinD with 5% MD for WBC quantification, while 47.5% had MinD with 2.5% MD for bacterial counts between EW and CP. 85% of bacterial count discrepancies represented increased bacterial counts by EW. Altered cell morphology was again observed in protocol B. Similar results were found when comparing EM to CP in the two protocols.

2) Culture Results: Protocol A: For final report, there were 60.5% MinD and 3.5% MD between EW and CP. For Protocol B, no MD was identified with 85% MinD between EW and CP. Similar results were observed between EM and CP. In specimens with MinD for bacterial growth, more colonies from the Eswab and better isolation in EW were observed.

Conclusions

Eswabs improved bacterial yield from Gram smear and culture compared to semi-solid swabs. EW showed better colony isolation. Some cell morphology changes in Eswab specimens might impact the interpretation of intracellular bacteria and differentiation between WBCs and RBCs. Gram smear competence training is important for the transition from semi-solid swabs to Eswabs.