1804. Impact of Susceptibility Testing Method on Antibiotic Selection for Methicillin-Resistant Staphylococcus Aureus (MRSA) Bacteremia
Session: Poster Abstract Session: Antimicrobial Stewardship: Impact of New Diagnostics
Saturday, October 6, 2018
Room: S Poster Hall
  • IDWeek Poster (Mahesh Bhatt, University of Kentucky).pdf (185.6 kB)
  • Background:

    The selection of intravenous (IV) antibiotics for Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia can be influenced by the vancomycin minimum inhibitory concentration (MIC). This study explores the changes in antibiotic use and inpatient mortality for patients with MRSA bacteremia after switching the MIC testing methods.


    At University of Kentucky Medical Center, Etest™ was implemented in 11/2013 for all Staphylococcus aureus blood isolates. In 4/2016, this was changed to Phoenix™ automated system. Data regarding antibiotic usage for patients with MRSA bacteremia were collected from 7/2014 to 12/2015 (Etest™) and 9/2016 to 3/2017 (Phoenix™). Only patients started on IV vancomycin were included. Daptomycin and ceftaroline use was monitored by the antimicrobial stewardship team with focus on guideline adherence.


    A total of 119 and 62 patients were identified before and after switching to Phoenix™. MICs of 2 mcg/ml were significantly decreased (P <0.001) after changing to Phoenix (Table 1). Daptomycin use (alone or in combination) decreased from 37% (44/119) to 21% (13/62) (p=0.013). Ceftaroline use (alone or in combination) decreased from 32% (38/119) to 19% (12/62) (p=0.036). The reason for escalation in 13 of 44 (30%) patients with daptomycin and 6 of 38 (16%) patients with ceftaroline was a MIC of 2 mcg/ml. Overall, IV vancomycin use (alone or in combination) increased from 50% (60/119) to 69% (43/62) (p=0.007). All-cause inpatient mortality was 16% (19/119) before and 10% (6/62) (p=0.24) after switching to Phoenix.


    A switch in vancomycin susceptibility testing from Etest™ to Phoenix™ automated system was associated with a significant decrease in daptomycin and ceftaroline use and an increase in IV vancomycin use without any change in all-cause inpatient mortality.

    Table 1.  Difference in MIC data and antibiotic utilization


    Etest™ (n=119)

    n (%)

    Phoenix™ (n=62)

    n (%)

    P value

    MIC = 2 mcg/ml

    56 (47) 

    2 (3)


    MIC = 1.5 mcg/ml

    37 (31)



    MIC ≤1 mcg/ml

    26 (22)

    60 (97)


    IV vancomycin

    60 (50)

    43 (69)



    44 (37)

    13 (21)



    38 (32)

    12 (19)


    *Other antibiotics

    4 (3)

    4 (6)


    All-cause inpatient mortality

    19 (16)

    6 (10)


    * Include linezolid and trimethoprim/sulfamethoxazole


    Mahesh Bhatt, MBBS1, Donna R. Burgess, RPh2,3, Katie L. Wallace, PharmD, BCPS2,3, Eric Gregory, PharmD3 and Thein Myint, MBBS4, (1)Infectious Diseases, University of Kentucky, Lexington, KY, (2)University of Kentucky, College of Pharmacy, Lexington, KY, (3)University of Kentucky HealthCare, Lexington, KY, (4)Division of Infectious Diseases, University of Kentucky, Lexington, KY


    M. Bhatt, None

    D. R. Burgess, None

    K. L. Wallace, None

    E. Gregory, None

    T. Myint, None

    Findings in the abstracts are embargoed until 12:01 a.m. PDT, Wednesday Oct. 3rd with the exception of research findings presented at the IDWeek press conferences.