title: Antimicrobial susceptibility of Staphylococcus aureus and molecular epidemiology of meticillin-resistant S. aureus isolated from Australian hospital inpatients: Report from the Australian Group on Antimicrobial Resistance 2011 Staphylococcus aureus Surveillance Programme.
abstract: The Australian Group on Antimicrobial Resistance (AGAR) performs regular multicentre period prevalence studies to monitor changes in antimicrobial resistance. In 2011, 29 laboratories in Australia participated in the national surveillance of Staphylococcus aureus resistance. The survey only included unique isolates from clinical specimens collected ≥48h after hospital admission. MRSA accounted for 30.3% of S. aureus isolates. MRSA resistance to ciprofloxacin, erythromycin, tetracycline, trimethoprim/sulfamethoxazole, gentamicin and clindamycin (constitutive resistance) varied considerably between regions. Resistance to non-β-lactam antimicrobials was uncommon in MSSA, with the exception of erythromycin. Regional variation in resistance was due to the differential distribution of MRSA clones between regions. The proportion of S. aureus genetically characterised as healthcare-associated MRSA (HA-MRSA) was significantly lower in this survey (18.2%) compared with the 2005 survey (24.2%) (P<0.0001). Although four HA-MRSA clones were characterised, 98.8% of HA-MRSA were classified as either ST22-MRSA-IV [2B] (EMRSA-15) or ST239-MRSA-III [3A] (Aus-2/3 EMRSA). Multiclonal community-associated MRSA (CA-MRSA) increased markedly from 6.5% in 2005 to 11.7% of all S. aureus in 2011 (P<0.0001). Although the proportion of MRSA resistant to non-β-lactam antimicrobials has decreased nationally, the proportion of S. aureus that are MRSA has remained stable. This is primarily due to non-multiresistant CA-MRSA becoming more common in Australian hospitals at the expense of the long-established multiresistant ST239-MRSA-III [3A] (Aus-2/3 EMRSA). Given hospital outbreaks of CA-MRSA are thought to be extremely rare, it is most likely that patients colonised at admission with CA-MRSA have become infected with the colonising strain during their hospital stay.
authors.affiliation: Department of Microbiology and Infectious Diseases, Royal Perth Hospital, PathWest Laboratory Medicine - WA, Perth, Western Australia, Australia; Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia. Electronic address: geoffrey.coombs@health.wa.gov.au.
authors.forename: Geoffrey W
authors.initials: GW
authors.lastname: Coombs
authors.affiliation: Department of Microbiology and Infectious Diseases, Royal Perth Hospital, PathWest Laboratory Medicine - WA, Perth, Western Australia, Australia.
authors.forename: Julie C
authors.initials: JC
authors.lastname: Pearson
authors.affiliation: Division of Microbiology, Pathology Queensland Central Laboratory, Herston Hospitals Campus, Herston, Queensland, Australia.
authors.forename: Graeme R
authors.initials: GR
authors.lastname: Nimmo
authors.affiliation: Infectious Diseases Unit and Microbiology Department, The Canberra Hospital, Garran, Australian Capital Territory, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Collignon
authors.affiliation: SA Pathology, Department of Microbiology and Infectious Diseases, Women's and Children's Hospital, North Adelaide, South Australia, Australia.
authors.forename: Jan M
authors.initials: JM
authors.lastname: Bell
authors.affiliation: Healthcare Associated Infection and Infectious Diseases Control, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Mary-Louise
authors.initials: ML
authors.lastname: McLaws
authors.affiliation: Department of Microbiology and Infectious Diseases, Royal Perth Hospital, PathWest Laboratory Medicine - WA, Perth, Western Australia, Australia; Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia.
authors.forename: Keryn J
authors.initials: KJ
authors.lastname: Christiansen
authors.affiliation: SA Pathology, Department of Microbiology and Infectious Diseases, Women's and Children's Hospital, North Adelaide, South Australia, Australia.
authors.forename: John D
authors.initials: JD
authors.lastname: Turnidge
keywords: Hospital inpatients; MRSA; MSSA; Period prevalence studies; Staphylococcus aureus