310 - The Impact of Microscan versus Vitek-2 for Automated Susceptibility Testing on the Utilization of Vancomycin Alternatives for the Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia

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Co-Author(s)

AM

Alexander Moskhos

Doctor of Pharmacy Candidate
College of Pharmacy, The University of Texas at Austin, Austin, TX
Austin, Texas
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
AW

Arya Wibisono

Doctor of Pharmacy Candidate
College of Pharmacy, The University of Texas at Austin, Austin, TX
Austin, Texas
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Kelly R. Reveles

Associate Professor
The University of Texas at Austin
San Antonio, Texas
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.

Presenting Author(s)

Dusten T. Rose

Network Infectious Diseases Clinical Pharmacist
Ascension Texas, Dell Seton Medical Center at The University of Texas, Department of Pharmacy, Austin, TX
Austin, Texas
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.

Background: Automated susceptibility testing (AST) provides minimum inhibitory concentrations (MIC) to guide effective antibiotic therapy. AST is critical for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, as susceptible MIC values ≥ 1.5 µg/mL are associated with vancomycin (VAN) failure. The Microscan (MS) instrument may report elevated MIC values compared to Vitek-2 (VTK), thus impacting treatment. This study aimed to evaluate the impact of MS versus VTK on VAN alternative use in the treatment of MRSA bacteremia in a Texas health system.

Methods: This was a retrospective cohort study of patients admitted to the Ascension Seton health system in Austin, TX. Patient eligibility included: age ≥18 years, ≥1 positive MRSA blood culture, ≥72 hours of MRSA therapy, and VAN use within 48 hours of positive culture. Patients were stratified into the MS group (May 2013-Dec 2016) and VTK group (Jun 2017-Mar 2020). The primary outcome was therapy switch from VAN to VAN alternatives. Secondary endpoints include S. aureus MIC, 30-day all-cause mortality, 30 and 90-day readmission, and length of hospital stay (LOS). Outcomes were compared between groups using appropriate bivariable comparisons, as well as multivariable logistic regression and propensity score-adjusted logistic regression.

Results: A total of 199 patients were included: 91 in the MS group and 108 in the VTK group. Switch to VAN alternative was 56% vs. 19% (p< 0.0001) for MS and VTK, respectively. The median (interquartile range) MIC value reported was 2 μg/mL (2 – 2) and 1 μg/mL (0.5 – 1) for MS and VTK, respectively (p< 0.0001). Thirty-day readmission (19% vs. 20%, p=0.7647) and 30-day mortality (10% vs. 9%, p=0.5262) were comparable between MS and VTK groups, respectively. Hospital LOS significantly decreased in the VTK period (16 days vs. 12 days, p=0.0153). The MS group was the only independent positive predictor of VAN alternative therapy: logistic regression, OR 5.64 (95% CI 1.67-18.99) and propensity score adjusted, OR 4.21 (95% CI 1.32-13.48).

Conclusion: Since implementation of VTK from MS, Ascension Seton hospitals experienced a decreased median VAN MIC for MRSA bacteremia as well as therapy switches from VAN to VAN alternatives without affecting other patient health outcomes.