1250. USA300 methicillin-resistant Staphylococcus aureus (MRSA) emerging as a cause of blood stream infection in tertiary military medical centers
Session: Poster Abstract Session: Staphylococcal Resistance and Epidemiology
Saturday, October 22, 2011
Room: Poster Hall B1
Background:  USA300 methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of skin and soft-tissue infection (SSTI) in military personnel living in community settings.  In civilian metropolitan healthcare centers, USA300 MRSA has emerged as a common cause of healthcare-associated blood stream infection (BSI). The contribution of USA300 MRSA to BSI in tertiary military medical centers has not been defined.

Methods:  Walter Reed Army Medical Center (WRAMC) and National Naval Medical Center (NNMC) are tertiary military medical centers that receive wounded military personnel from combat theaters and care for military beneficiaries.  These centers have approximately 500 inpatient beds combined.  We conducted a retrospective case-control study in adult patients with MRSA BSI at WRAMC and NNMC from 2001 to 2009.  Pulse-field gel electrophoresis (PFGE) was completed on MRSA isolates in concert with record review to determine the prevalence and risk factors for USA300 MRSA BSI.

Results:  From 2001 to 2009 there were 245 documented cases of MRSA BSI at these two institutions.  152 isolates were available for analysis.  Epidemiological characteristics of the 152 cases included a mean age of 61 years, 70% were male, 62% were Caucasian, and 11% were combat-wounded.  The crude in-hospital mortality rate for MRSA BSI was 17%.  Overall, we found that 30 (20%) of the 152 MRSA BSI cases were USA300; and 26 (87%) of these 30 USA300 BSI cases were healthcare-associated.  When examined over progressive three-year time periods, USA300 represented a significantly increasing proportion of isolates:  2 (4%) of 51 from 2001 to 2003; 9 (19%) of 48 from 2004 to 2006; and 19 (36%) of 53 from 2007 to 2009 (p < .001, Fisher’s Exact Test).  There appeared to be no discriminating risk factors for USA300 BSI in our patient population.  In particular, USA300 was not associated with combat wounds or skin and soft-tissue infection.

Conclusion:   USA300 MRSA is emerging as a significant cause of healthcare-associated MRSA BSI in tertiary military medical centers.  However, patients with combat wounds and those with skin and soft-tissue infection do not seem to be contributing to this trend.  Further studies are needed to examine the changing epidemiology of this pathogen.

Subject Category: C. Clinical studies of bacterial infections and antibacterials including sexually transmitted diseases and mycobacterial infections (surveys, epidemiology, and clinical trials)

Jeffrey Sherwood, MD1, Matthew Park, MD1, Paul Robben, MD1, Richard Shoemaker, MD, MPH1, Marvele Tshimanga1, Britta Babel, MS2, Timothy Whitman, DO2 and Michael Ellis, MD3, (1)Walter Reed Army Medical Center, Washington, DC, (2)National Naval Medical Center, Bethesda, MD, (3)Uniformed Services University of the Health Sciences, Bethesda, MD


J. Sherwood, None

M. Park, None

P. Robben, None

R. Shoemaker, None

M. Tshimanga, None

B. Babel, None

T. Whitman, None

M. Ellis, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.