Rapid Phenotypic Susceptibility Testing May Improve Bacteremia Management

Septicemia Sepsis
New data demonstrate the potential of the Accelerate Pheno™ system to improve antimicrobial use and stewardship.

Data published in The Journal of Antimicrobial Chemotherapy demonstrate the potential of the Accelerate Pheno™ system (AXDX) to improve antimicrobial use and stewardship.

The AXDX system’s performance and time to result for pathogen identification and antimicrobial susceptibility testing were compared with current standard of care methods using clinical samples from patients with monomicrobial gram-negative bacteremia.

The mean pathogen identification time for the standard of care methods of the Bruker MALDI Biotyper® and the VERIGENE® systems were 21 and 4.4 hours, respectively. Mean pathogen identification time using AXDX in comparison was 3.7 hours. When comparing mean antimicrobial susceptibility testing time between AXDX and the VITEK 2 system, the results were 9.0 hours for AXDX and 35 hour for VITEK 2. The positive and negative percentage agreement for pathogen identification was 95.9% and 99.9%, respectively. Regarding antimicrobial susceptibility testing, the essential agreement was 94.5% and categorical agreement was 93.5%.

Using chart reviews, investigators also calculated theoretic times to antibiotic de-escalation and escalation as well as active and optimal therapy. Results of these calculations determined that if AXDX results were available, 25% of patients could be on active therapy faster, and 78% of patients who had therapy optimized during hospitalization could have reached this goal faster. Further, the time to de-escalation might have been reduced from 31 hours to 16 and escalation time reduced from 31 hours to 19 compared with standard of care.

Investigators cautioned that the results may be less generalizable as the study was performed at a single center with multiple state-wide satellite hospitals that care for a wide variety of patients including individuals who are immunocompromised and a population with a broad spread of resistance patterns. The study population was also limited to gram-negative infections and did not address gram-positive or yeast blood stream infections. There was also a lack of polymicrobial infections tested which may have enhanced the performance of AXDX with respect to previous studies. Investigators also noted that several assumptions were required regarding the clinical effect of time to results, which may have influenced the ability to infer true result times and clinical impact. Further, there is variation in optimal or institution preferred therapies and the overall costs were not assessed. Investigators also recommended that “clinical studies comparing AXDX with rapid diagnostic tests implemented at other laboratories, specifically those that include molecular antimicrobial susceptibility testing, are needed to evaluate the true impact of AXDX’s phenotypic [antimicrobial susceptibility testing] results.”

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These findings underscore the potential clinical benefits of rapid phenotypic susceptibility testing to allow earlier modification of empiric therapy. Although the true clinical significance of the time to results differences shown here are unknown, investigators believe that given prior evidence that each hour of delayed treatment for gram-negative bacteremia increases mortality, “it stands to reason that these time differences could have a significant clinical impact.”


Schneider JG, Wood JB, Schmitt BH, et al. Susceptibility Provision Enhances Effective De-escalation (SPEED): utilizing rapid phenotypic susceptibility testing in Gram-negative bloodstream infections and its potential clinical impact. J Antimicrob Chemother. 2019;74:i16-i23.

This article originally appeared on Infectious Disease Advisor