565. Comparison of MRSA Clinical and Carriage Isolates in Colonized Veterans
Session: Poster Abstract Session: MRSA Surveillance and Infection Prevention
Friday, October 21, 2011
Room: Poster Hall B1
  • FINAL_Stenehjem_Satola_565.pdf (504.4 kB)
  • Background: Methicillin-resistant Staphylococcus aureus (MRSA) has undergone rapid evolutionary changes and epidemiologic expansion. Few studies have evaluated the strain characteristics of colonizing and disease-causing isolates in patients over time. Methods: MRSA isolates from Atlanta VA Medical Center patients with clinical infections (inpatient and outpatient) and discharge nasal colonization were collected since Jan 2010. MRSA was isolated from admission PCR-positive nasal swabs using SPECTRA agar since Jan 2011. Cycle times were recorded on PCR-positive swabs and quantitative cultures were performed on nasal colonization cultures. A subset of patients with both one or more clinical infection and nasal isolates were identified. All isolates (clinical and nasal) were typed by standard PFGE methods. Results: Between 1/2010 - 4/2011, 1002 nasal and 351 clinical infection MRSA isolates from 675 unique patients were collected. At least one clinical infection and a nasal colonization isolate from the same patient were available for PFGE typing in 77 patients. 114 isolates from 22 patients were PFGE typed. The average number of isolates (clinical and nasal) per patient was 5.3 (range 2 - 11) with an average duration between first and last culture of 195 days (1 - 381 days). In 21 of 22 (95%) patients, PFGE types matched for all clinical infection and colonization isolates. One patient, with only 2 isolates available, 4 months apart, had different types. Twelve patients were colonized with USA100, 7 with USA300, 3 with USA500. Most (6 of 7) patients colonized with USA300 had skin or soft tissue infections; USA100 carriers had 6 urinary tract, 4 bloodstream, and 4 respiratory infections; USA500 carriers had 1 skin and 2 respiratory infections. No difference was noted in admission PCR cycle time (p = 0.6) or quantitative culture results (p=0.8) among patients colonized with USA100 and USA300. Conclusion: MRSA PFGE type remained very consistent over the course of follow up for the majority of patients followed. Infection and colonization were the same MRSA strain in 95% of patients observed. No appreciable difference in nasal bacterial burden was observed between USA100 and USA300 colonizing strains in patients with clinical MRSA infections.

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

    Edward Stenehjem, MD1, David Rimland, MD2, Monica Farley, MD2, Emily Crispell3 and Sarah W. Satola1, (1)Emory University School of Medicine and Atlanta VA Medical Center, Decatur, GA, (2)Atlanta VA Medical Center and Emory University School of Medicine, Decatur, GA, (3)Atlanta Research and Education Foundation, Decatur, GA


    E. Stenehjem, None

    D. Rimland, None

    M. Farley, None

    E. Crispell, None

    S. W. Satola, 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.