1804. Impact of Susceptibility Testing Method on Antibiotic Selection for Methicillin-Resistant Staphylococcus Aureus (MRSA) Bacteremia

Abstract

BackgroundThe 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.MethodsAt University of Kentucky Medical Center, Etest™ was implemented in November 2013 for all Staphylococcus aureus blood isolates. In April 2016, this was changed to Phoenix™ automated system. Data regarding antibiotic usage for patients with MRSA bacteremia were collected from July 2014 to December 2015 (Etest™) and September 2016 to March 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.ResultsA total of 119 and 62 patients were identified before and after switching to Phoenix™. MICs of 2 μg/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 an MIC of 2 μg/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.Table 1:Difference in MIC Data and Antibiotic UtilizationParametersEtest™ (n = 119) n (%)Phoenix™ (n = 62) n (%) P-ValueMIC = 2 μg/mL56 (47)2 (3)<0.001MIC = 1.5 μg/mL37 (31)N/AN/AMIC ≤1 μg/mL26 (22)60 (97)<0.001IV vancomycin60 (50)43 (69)0.007Daptomycin44 (37)13 (21)0.013Ceftaroline38 (32)12 (19)0.036Other antibioticsa4 (3)4 (6)0.27All-cause inpatient mortality19 (16)6 (10)0.24 aInclude linezolid and trimethoprim/sulfamethoxazole.ConclusionA 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.Disclosures All authors: No reported disclosures.