1222. Risk Factors and Outcomes for Daptomycin Nonsusceptible Methicillin-Resistant Staphylococcus aureus Bloodstream Infections

Abstract

BackgroundDaptomycin (dap) has been approved and successfully used for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. However, reports of daptomycin nonsusceptible (DNS) MRSA strains have emerged over the recent years. This study describes the clinical characteristics of patients with DNS MRSA bloodstream infections (BSIs) with the objective of identifying risk factors and outcomes.MethodsThis is a retrospective case–control study in a tertiary healthcare system in southeast Michigan. Cases included 34 patients with DNS MRSA BSI between September 24, 2005 and March 31, 2018. Cases were matched with controls with MRSA BSI based on age, source of BSI, and time-period of BSI in a 1:1 ratio. Charts were reviewed for clinical and laboratory data. Vancomycin (van) and dap minimum inhibitory concentrations (MICs) were determined by E-test. DNS was defined as an MIC >1.0 µg/mL. Chi-square test, Fisher’s exact test, and t-test were used to determine statistical significance.ResultsIn the case cohort, the source of BSI was endovascular in 11(32%) patients, central-line associated in 3(9%), secondary BSI in 13(38%), and unknown in 7(21%). Table 1 is a summary of the results.Table 1. Clinical Characteristics and Outcomes of Cases and ControlsCasesControls N = 34(%) N = 34(%) P-valueMean age (SD)63.5 (12.0)61.9 (11.2)0.572Male18 (52.9)21 (61.8)0.462Mean bacteremia duration in days (SD)4.4 (3.2)5.9 (4.9)0.195Mean LOS in days (SD)19.5 (13.6)18.4 (14.6)0.751Mean van MIC (SD)2.04 (1.19)1.39 (0.36)0.003Mean dap MIC (SD)2.69 (1.32)0.57 (0.24)<0.0001Epidemiologic acquisitionCommunity-acquired0 (0)9 (26.5)0.002Healthcare-associated21 (63.6)22 (64.7)0.927Hospital-acquired12 (36.4)3 (8.8)0.00790-day prior dap exposure23 (82.1)3 (9.7)<0.0001Mean dap exposure in days23.6 (21.0)2.68 (10.6)<0.000190-day prior van exposure25 (89.3)9 (29)<0.0001Mean van exposure in days13.0 (14.7)4.19 (12.7)0.02030-day mortalitya10 (32.3)6 (18.8)0.218Mean Charlson Comorbidity Index (SD)5.7 (3.07)4.4 (2.9)0.07790-day MRSA BSI recurrencea8 (44.4)2 (9.5)0.025 aFrom date of index BSI.ConclusionPrior exposure to dap and van, and higher van MIC in MRSA isolates are risk factors for DNS MRSA BSI. DNS is associated with significantly higher risk of 90-day MRSA BSI recurrence.Disclosures All authors: No reported disclosures.