Dissemination of USA300 MRSA in Western 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 dissemination of USA300 MRSA (ST8-MRSA-IV) in Australia.

    Background: In Western Australia (WA) all MRSA are referred to the Gram-Positive Bacteria Typing and Research Unit. In 2003 a ST8-MRSA-IV isolate with a pulsotype similar to WA MRSA-5 (dendrogram similarity of 77%) was characterised and classified as WA MRSA-12. From 2005 to 2007 a further 69 WA MRSA-12 from 62 patients were identified. Skin and soft tissue infection (predominantly boils and ulcers) was a frequently encountered clinical picture. Retrospective testing of ST8-MRSA-IV isolates characterised two strains: WA MRSA-12 which were were PVL positive by PCR and had the same pulsotype, coagulase PCR-RFLP type (18) and spa type (t008) as a reference strain of USA300 MRSA; and WA MRSA-5 which were PVL negative.

    Methods: MRSA were characterised by antibiogram, coagulase PCR-RFLP, PFGE, PVL PCR, spa typing, MLST and SCCmec typing.

    Results: From July 2003 to March 2008 89 MRSA from 78 patients were characterised as USA300 MRSA. 82 (92%) of these isolates caused skin and soft tissue infections predominantly with abscess formation. The remaining seven isolates were from nasal screening swabs (4) including one from a health care worker, respiratory samples (2) and one from an unspecified source. Over 60% of patients were younger than 40 years. 76 (85%) isolates were erythromycin resistant (EmR), 35 (39%) ciprofloxacin resistant, nine (10%) tetracycline resistant and five (6%) mupirocin resistant. Resistance to trimethoprim, gentamicin, rifampicin and fusidic acid was not detected. Of the EmR strains 88% were clindamycin susceptible (inducible resistance not detected – unlike EmR WA MRSA-5 which are inducibly resistant to clindamycin).

    Conclusions: In the United States USA300 MRSA is the predominant cause of community associated infection and is rapidly emerging as a major cause of healthcare associated infection. Although most clinical presentations have been skin and soft-tissue infections, life-threatening infections such as necrotizing pneumonia and sepsis have frequently been reported. In WA the number of USA300 MRSA per year (2003 to 2007) increased several-fold (7, 8, 17, 30 new cases respectively) prompting public health concern. The WA Department of Health has recently commenced a "Search and Destroy" policy aimed at preventing the spread of USA300 in both the community and hospital setting.