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Performance of the Qvella FASTTM Prep System in the Analysis of Positive Blood Cultures

Brody Dams1, Carrie Maro2, Kristina Helm2, Benjamin von Bredow, D(ABMM), M(ASCP)CM2

  1. Oakland University William Beaumont School of Medicine, Rochester, MI, USA
  2. Division of Microbiology, Department of Pathology, Corewell Health, Royal Oak, MI, USA

Introduction

  • Sepsis is a life-threatening dysregulated systemic inflammatory response to a bloodstream infection
  • Studies show that earlier initiation of antibiotics leads to lower mortality, and current clinical guidelines recommend empiric antibiotics within 3 hours1-4
  • Identification and susceptibility testing can take 48-72 hours with standard of care (SoC) culturing methods
  • The Qvella FASTTM Prep System (Qvella) can potentially reduce this time by 18-24 hours by producing a Liquid ColonyTM (LC) when blood cultures are flagged positive

Aims and Objectives

  • To assess the performance of the Qvella in the analysis of positive blood cultures by comparing the accuracy of microbial species identification and antimicrobial resistance detection to the standard of care.

Methods

  • Positive blood cultures were retrospectively run on the Qvella to produce an LC in <1 hour
  • The LC was then used for identification (ID) on MALDI-TOF and used as inoculum for antibiotic susceptibility testing (AST)
  • ID and AST results were then compared between the LC and standard of care

Qvella FASTTM Prep System5

Results

  • MALDI-TOF results from the LC agreed with the SoC at the genus or species level in 69% (62/90) of samples (Table 1)
  • In 31% (28/90) of samples, no ID was obtained from the LC (Table 1)
  • Overall essential agreement (EA) and categorical agreement (CA) for AST was 97.9% and 94.9% for Gram (-) species, respectively (Table 2)
  • Very Major Error (VME) rate was 1.1%, Major Error (ME) rate was 2.2%, and Minor Error (miE) rate was 3.0% for Gram (-) species (Table 2)
  • Overall EA and CA for AST was 96.1% and 95.8% for Gram (+) species, respectively (Table 3)
  • VME rate was 9.3%, ME rate was 1.5%, and miE rate was 1.6% for Gram (+) species (Table 3)

Table 1, MALDI-TOF ID Results for LC

Table 1. For Coagulase negative staph, many of these were not identified to the species level

Table 2, Gram (-) Species AST Results

Table 2. EA: essential agreement. CA: categorical agreement. VME: very major error. ME: major error. miE: minor error. Interpretive results are not available for nitrofurantoin. VME for Tigecycline could not be calculated due to a lack of resistant isolates.

Table 3, Gram (+) Species AST Results

Table 3. EA: essential agreement. CA: categorical agreement. VME: very major error. ME: major error. miE: minor error. Error rates are not applicable for Inducible Clindamycin and Cefoxitin Screen. VME could not be calculated for several drugs due to a lack of resistant isolates.

Conclusions

  • Gap in ID accuracy was largely due to significant number of failed runs with the LC
  • When an ID result was achieved with the LC on MALDI-TOF, results were highly accurate
  • In many cases, samples required several MALDI-TOF runs to generate a result
  • CA for specific drugs was below our acceptable threshold (≥90%), which could be addressed with more targeted testing
  • Very Major rates above our acceptable threshold (≤3%) was likely due to a small number of resistant isolates being tested
  • The Qvella LC represents a promising technology for reducing times to species ID and AST patterns from blood cultures
  • More work is needed to address the high failure rate of ID on MALDI-TOF

References

  1. Peltan ID, Brown SM, Bledsoe JR, et al. ED Door-to-Antibiotic Time and Long-term Mortality in Sepsis. Chest. 2019;155(5):938-946. doi:10.1016/j.chest.2019.02.008
  2. Seymour CW, Gesten F, Prescott HC, et al. Time to Treatment and Mortality during Mandated Emergency Care for Sepsis. N Engl J Med. 2017;376(23):2235-2244. doi:10.1056/NEJMoa1703058
  3. Liu VX, Fielding-Singh V, Greene JD, et al. The Timing of Early Antibiotics and Hospital Mortality in Sepsis. Am J Respir Crit Care Med. 2017;196(7):856-863. doi:10.1164/rccm.201609-1848OC
  4. Evans L, Rhodes A, Alhazzani W, et al. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Crit Care Med. 2021;49(11):e1063-e1143. doi:10.1097/CCM.0000000000005337
  5. Kuo P, LeCrone K, Chiu M, Realegeno S, Pride DT. Analysis of the FAST™ system for expedited identification and antimicrobial susceptibility testing of bloodborne pathogens. Diagn Microbiol Infect Dis. 2022;104(4):115783. doi:10.1016/j.diagmicrobio.2022.115783