1750. Changes in Incidence and Strains of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections, 2005–2013
Session: Oral Abstract Session: MRSA Prevention and Epidemiology
Saturday, October 29, 2016: 9:45 AM
Room: 288-290
Background: Although healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) incidence has decreased over the past decade in the US, primarily single-center studies in 2013 and earlier suggest that USA300 "community" strains are becoming increasingly common in healthcare.  We estimated USA100 (the traditional "healthcare" strain) and USA300 BSI incidence on a population level from multistate data to characterize their role in MRSA BSIs from 2005-2013.

Methods: MRSA BSI cases and corresponding isolates included in the analysis were reported from 14 hospitals in 5 states to the CDC Emerging Infections Program’s (EIP’s) active, laboratory- and population-based MRSA surveillance from 2005-2013 and classified as hospital-onset, healthcare-associated community-onset, or community-associated based on healthcare exposures and timing of infection.  Isolates were typed by pulsed-field gel electrophoresis or a validated algorithm for inferring USA type.  Strain-specific incidence among patients presenting to these hospitals (per 100,000 population) was estimated using statistical weighting based on distribution of strains among cases with strain-typed isolates accounting for site, year, and epidemiologic classification.

Results: Isolates were obtained for 3790 of the 5614 MRSA BSIs (67.5%) reported to EIP.  From 2005-2013, estimated USA100 incidence decreased primarily for hospital-onset (6.2 vs 1.1 / 100,000 persons, P<0.05) and healthcare-associated, community-onset (10.7 vs 4.8 / 100,000 persons P<0.05) BSIs (Figure).  In contrast, incidence of hospital-onset USA300 decreased (1.6 vs 0.4 / 100,000 persons, P<0.05) but incidence did not significantly change for healthcare-associated, community-onset (3.8 vs 3.7 / 100,000 persons, P>0.05) or community-associated USA300 (2.7 vs 2.5 / 100,000 persons, P>0.05).  Although incidence of USA300 decreased from 2005-2013, estimated % of all MRSA BSIs due to USA300 increased from 26% to 37%

Conclusion: Population-based incidence of USA300 BSIs did not increase in any epidemiologic category.  The fraction of MRSA BSIs that were USA300 increased due to greater declines in USA100 BSI incidence.  However, given lack of decline in incidence, strategies to prevent USA300 MRSA BSIs in the community are particularly needed to ensure future declines in MRSA BSI incidence.

Isaac See, MD1, Valerie Albrecht, MPH1, Yi Mu, PhD1, Ghinwa Dumyati, MD, FSHEA2, Mackenzie Koeck, MPH3, Ruth Lynfield, MD, FIDSA3, Joelle Nadle, MPH4, Susan M. Ray, MD, FIDSA5, William Schaffner, MD, FIDSA, FSHEA6, Brandi Limbago, PhD1 and Alexander Kallen, MD, MPH1, (1)Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, Atlanta, GA, (2)University of Rochester Medical Center, Rochester, NY, (3)Minnesota Department of Health, St. Paul, MN, (4)California Emerging Infections Program, Oakland, CA, (5)Division of Infectious Diseases, Emory University School of Medicine, Atlanta, GA, (6)Vanderbilt University School of Medicine, Nashville, TN


I. See, None

V. Albrecht, None

Y. Mu, None

G. Dumyati, None

M. Koeck, None

R. Lynfield, None

J. Nadle, None

S. M. Ray, None

W. Schaffner, None

B. Limbago, None

A. Kallen, None

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