International MRSA clones identified in Western Australia

  • Hui-Leen Tan, PathWest Laboratory Medicine, Royal Perth Hospital, Australia
  • Julie Pearson, PathWest Laboratory Medicine, Royal Perth Hospital, Australia
  • Mr Geoffrey Coombs, PathWest Laboratory Medicine, Royal Perth Hospital, Australia
  • A/Prof Keryn Christiansen, PathWest Laboratory Medicine, Royal Perth Hospital, Australia
  • Dr Ronan Murray, PathWest Laboratory Medicine, Royal Perth Hospital, Australia
  • Dr James Robinson, PathWest Laboratory Medicine, Royal Perth Hospital, Australia
  • Frances O'Brien, Curtin University of Technology, Australia

    • Objective: To report the emergence of international MRSA clones in Western Australia.

    Background: Several international healthcare-associated MRSA clones have caused outbreaks in Western Australian (WA) hospitals however a state-wide MRSA management programme has prevented these clones from becoming endemic in WA acute-care hospitals. In recent years, several international community-associated MRSA (CA-MRSA) clones have been detected in WA. Unlike WA CA-MRSA, these international clones harbour the Panton-Valentine leukocidin (PVL) gene which is associated with high virulence potential.

    Methods: In WA all clinical isolates of MRSA are referred to the Gram-positive Bacteria Typing and Research Unit (GPBTRU) for epidemiological typing. Isolates are characterised by phenotypic and molecular methods including antibiogram, coagulase-gene PCR-RFLP, PVL PCR, pulsed-field gel electrophoresis, spa typing, multi locus sequence typing (MLST) and SCCmec typing.

    Results: From July 2003 to December 2007, 16,094 MRSA were referred to the GPBTRU. 3,494 (21.8%) were identified as “international MRSA clones”. Seven international healthcare-associated MRSA were characterised: ST8-MRSA-II (Irish-1 EMRSA), ST8-MRSA-VI (Irish-2 EMRSA), ST5-MRSA-II (New York/Japan MRSA), ST22-MRSA-IV (EMRSA-15), ST36-MRSA-II (EMRSA-16), ST247-MRSA-I (EMRSA-17) and ST228-MRSA-I (Southern German clone). First isolated in WA in 1997 ST22-MRSA-IV (EMRSA-15) has become established in long-term care facilities in WA and accounts for 18.3% of all MRSA in WA. The remaining international healthcare-associated MRSA clones collectively accounted for 1.2% of MRSA. Four international community-associated PVL-positive clones were characterised: ST30-MRSA-IV (Western Samoan MRSA), ST8-MRSA-IV (USA300 MRSA), ST59-MRSA-VT (Taiwan MRSA clone) and ST80-MRSA-IV (European clone MRSA). International PVL positive MRSA accounted for 2.2% of MRSA in WA and have increased in prevalence from 1.1% in 2004 to 3.6% in 2007. The largest increases in prevalence reported were for the ST30-MRSA-IV (Western Samoan MRSA) (0.9% to 2.4%) and ST8-MRSA-IV (USA300 MRSA) (0.2% to 0.8%) clones.

    Conclusions: The repeated introduction of international healthcare-associated MRSA clones into WA and the increasing prevalence of PVL-positive MRSA clones is of public health concern. The WA Department of Health has recently targeted PVL-positive MRSA as part of the “Search and Destroy” policy initially introduced to control the spread of healthcare-associated MRSA in acute-care hospitals. The policy involves the notification of patients and healthcare workers and the epidemiological typing of all MRSA isolates. Characterisation of MRSA by MLST and SCCmec typing using internationally recognised nomenclature is vital in detecting new healthcare-associated and virulent strains of MRSA.