title: Increased EMRSA-15 health-care worker colonization demonstrated in retrospective review of EMRSA hospital outbreaks.
abstract: BACKGROUND
  Health care worker (HCW) colonization with methicillin resistant Staphylococcus aureus (MRSA) is a documented cause of hospital outbreaks and contributes to ongoing transmission. At Royal Perth Hospital (RPH) it had been anecdotally noted that the increasing prevalence of EMRSA-15 appeared to be associated with increased HCW colonization compared with Aus2/3-EMRSA. Hence we compared HCW colonization rates during outbreaks of EMRSA-15 and Aus2/3-EMRSA at a single institution.
  
  
  METHODS
  We performed a retrospective review of EMRSA-15 and Aus2/3-EMRSA outbreaks from 2000-2009 at RPH, a quaternary hospital in Western Australia. Outbreak files were reviewed and relevant data extracted.
  
  
  RESULTS
  Ten EMRSA-15 outbreaks were compared with seven Aus2/3 outbreaks. The number of patients colonized was similar between EMRSA-15 and Aus2/3-EMRSA outbreaks (median 7 [range 3-20] and 11 [5-26], respectively; P = 0.07) but the number of HCWs colonized was significantly higher in EMRSA-15 outbreaks compared to Aus2/3-EMRSA outbreaks (median 4 [range 0-15] and 2 [1-3], respectively; P = 0.013). The percentage of HCWs colonized was also higher in EMRSA-15 outbreaks versus Aus2/3-EMRSA outbreaks (median 3.4% [range 0-5.5%] and 0.81% [0.56-2.2%], respectively; P = 0.013).
  
  
  CONCLUSIONS
  This study demonstrates a higher level of HCW colonization during EMRSA-15 outbreaks compared with Aus2/3-EMRSA outbreaks. This finding suggests that MRSA vary in their ability to colonize HCWs and contribute to outbreaks. MRSA type should be determined during outbreaks and future research should investigate the mechanisms by which EMRSA-15 contributes to increased HCW colonization.
authors.affiliation: Department of Microbiology and Infectious Diseases, PathWest Laboratory Medicine, Royal Perth Hospital, Perth, Western Australia, Australia. julie.hart@health.wa.gov.au.
authors.forename: Julie
authors.initials: J
authors.lastname: Hart
authors.forename: Keryn J
authors.initials: KJ
authors.lastname: Christiansen
authors.forename: Rosie
authors.initials: R
authors.lastname: Lee
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Heath
authors.forename: Geoffrey W
authors.initials: GW
authors.lastname: Coombs
authors.forename: J Owen
authors.initials: JO
authors.lastname: Robinson