An Association of MRSA USA 300 with Mortality in MRSA Bacteremia Público

Kempker, Russell Ryan (2010)

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An Association of MRSA USA 300 with Mortality in MRSA Bacteremia By Russell Ryan Kempker

Introduction: Evidence suggests MRSA USA 300 strains may have increased virulence; however, there are no clinical studies evaluating outcomes of MRSA bacteremia based on MRSA strain.

Methods: Population based-surveillance for MRSA Bacteremia in 8-county Atlanta from 2005-2008. Cases, defined as MRSA isolated from blood, were classified as healthcare-associated with hospital-onset (HAHO), healthcare-associated with community-onset (HACO), or community-associated (CA) disease. An epidemiological analysis was performed on the entire cohort while a survival analysis was performed on a nested cohort consisting of all MRSA cases for which isolates were evaluated with pulse field gel electrophoresis (PFGE). A cox proportional hazards model was used to determine the association of USA 300 genotype and other risk factors with mortality.

Results: A total of 4344 cases of MRSA bacteremia were identified; 2579 (59.4%) were HACO, 1144 (26.3%) HAHO; 601 (13.8%) CA, and 20 (0.5%) unclassified. Incidence rates of MRSA bacteremia showed a significant decrease over time from 33.9/100,000 in 2005 to 24.8/100,000 in 2008. Rates per 100,000 were highest in persons ≥ 65 years (133.0), blacks (45.2), males (33.7), and persons with AIDS (650.5). PFGE testing was performed on 1104 MRSA isolates. In multivariate analysis, USA 300 genotype was associated with increased in-hospital mortality (HR 1.63, 95% CI 1.19, 2.23). Increasing age, chronic liver disease, AIDS, pneumonia, bacteremia without an associated clinical syndrome, and septic shock were also risk factors for death. In a sub-analysis comparing MRSA bacteremia due to USA 300 vs. USA 100 strains, USA 300 was also associated with increased mortality (HR 1.79, 95% CI 1.24, 2.58).

Conclusions: MRSA bacteremia incidence declined over 4 years but remained high; the proportion with CA disease was significant and persons with HIV, > 65 years old, and blacks were disproportionately affected. Bacteremia due to USA 300 MRSA isolates was associated with increased case-fatality, suggesting that USA 300 strains may be more virulent.

An Association of MRSA USA 300 with Mortality in MRSA Bacteremia
Russell Kempker, MD.
Master of Science in Clinical Research
Advisor: Monica M. Farley, MD
Advisor: Susan Ray, MD
A thesis submitted to the Faculty of the
James T. Laney Graduate Studies of Emory University
in partial fulfillment of the requirements for the degree of
Master of Science
in Clinical Research

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