EMRSA-15 Bacteremia is not Associated with a Worse Outcome Compared with Bacteremia Caused by Multidrug-Resistant MRSA.

EMRSA-15 (ST22-MRSA-IV) is rapidly replacing the endemic ST239 health care-associated methicillin-resistant Staphylococcus aureus clone in Singapore. A one-year single-centre cohort study of inpatients with MRSA bacteremia was performed to determine if bacteremia caused by EMRSA-15 was associated with worse outcomes compared to bacteremia caused by the endemic ST239 strain. Strains were identified by antibiotypes, and subsequent validation was performed on a selected sample of MRSA strains via pulsed-field gel electrophoresis and staphylococcal chromosome cassette mec typing. Two hundred and twenty-eight patients with MRSA bacteremia were studied; Seventy-three were infected with EMRSA-15. EMRSA-15 and ST239-infected patients were similar regarding gender, frequencies of most co-morbidities, and risk factors for adverse outcomes. Similar numbers of EMRSA-15-infected and ST239-infected patients died (24.7% vs 27.1%, P=0.70) or developed complicated infections (41.1% vs 40.0%, P=0.88). After multivariate analysis, EMRSA-15 as a cause of bacteremia was not significantly associated with either death or development of complicated infections, although inappropriate therapy (5.45-fold, P<0.01) and a respiratory source of bacteremia (4.69, P<0.01) were independently associated with subsequent mortality. The increased propensity of EMRSA-15 for dissemination was not associated with increased virulence in our patients. Further work in determining the mechanisms by which highly transmissible MRSA spreads rapidly is required to better target infection control approaches at these important emerging MRSA clones.