Multicenter evaluation of the eQUANT system for use with disk diffusion AST of gram-negative bacteria directly from positive blood cultures

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Abstract
Bloodstream infections frequently cause sepsis, a condition that can lead to organ dysfunction and death. Rapid antimicrobial susceptibility testing (AST) results are critical for appropriate medical intervention and to either de-escalate or escalate antibiotics to appropriate therapy. We describe the results from a multicenter clinical study evaluating the performance of the eQUANT system (Avails Medical, Inc., Menlo Park, CA). The eQUANT system generates a 0.5 McFarland equivalent suspension, the eMcFarland, directly from a positive blood culture bottle for use with downstream disk diffusion AST, thereby saving up to 24 hours compared to traditional AST workflow. A combination of fresh, prospectively collected clinical (42) and contrived (525) blood cultures were tested, and results for disk diffusion using the Avails eQUANT eMcFarland suspension as the inoculum were compared to disk diffusion results the next day using the standard 0.5 McFarland suspension prepared from plate subculture. Thirteen species of gram-negative rods were evaluated against 12 antibiotics. From the 2,679 pairs of AST results, overall categorical agreement was 95.0%. Overall very major errors, major errors, and minor errors were 0.15%, 0.60%, and 4.48%, respectively. The Avails eQUANT system has the potential to significantly accelerate the standard of care by eliminating the need for subculture. IMPORTANCE: Rapid reporting of antimicrobial susceptibility test results for bacterial isolates from blood cultures is critical for timely implementation of optimal antimicrobial therapy and improves outcomes of sepsis patients. In this study, we demonstrate the accuracy and performance characteristics of the eQUANT system, which generates a 0.5 McFarland equivalent suspension, the eMcFarland, directly from a positive blood culture bottle for use with downstream disk diffusion antimicrobial susceptibility testing (AST). Using the eMcFarland suspension allows for accurate and standardized reporting of disk diffusion AST results from positive blood cultures.

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