Accelerate PhenoTest TM BC Kit Versus Conventional Methods for Identification and Antimicrobial Susceptibility Testing of Gram-Positive Bloodstream Isolates: Potential Implications for Antimicrobial Stewardship

Abstract

Background: The Accelerate PhenoTest^TM BC kit (AXDX) provides rapid organism identification (ID) and antimicrobial susceptibility testing (AST) results. Its potential role for antimicrobial stewardship is unknown. Objective: To compare the diagnostic accuracy of AXDX with conventional methods (CMs) and assess AXDX’s potential role for antimicrobial stewardship in patients with Gram-positive bloodstream infections (BSIs). Methods: This retrospective cohort study included adults with Staphylococcus aureus or Enterococcus spp BSIs from July 2014 to January 2016 at a tertiary care medical center. Available isolates were tested on AXDX, and ID and AST results from AXDX were compared with those from CMs (VITEK 2 or ETEST). The following antibiotics were assessed for categorical agreement (CA) and essential agreement (EA) between the methods: ampicillin and daptomycin (Enterococcus spp only), erythromycin and cefoxitin (S aureus only), linezolid, and vancomycin. Potential role of AXDX for stewardship was assessed via a retrospective audit by infectious diseases clinicians. Results: We included 231 patients with S aureus (n = 112) or Enterococcus spp (n = 119) BSIs, and 106 unique isolates were available for ID and AST performance analyses. Sensitivity and specificity of AXDX for ID were 98.0% and 99.5%, respectively. CA and EA for the tested antibiotics were >97%. In Monte Carlo simulations, AXDX coupled with stewardship personnel (either 24/7 or Monday to Friday) would have allowed unnecessary therapy to be stopped and active/targeted therapy to be started ≥24 hours sooner in >50% of patients. Conclusions: Compared with CMs, AXDX had similar diagnostic accuracy and can potentially optimize therapy sooner in patients with Gram-positive BSIs.