Clinical features of invasive community-onset methicillin-resistant Staphylococcus aureus infection: prospective case-control study

  • Michael Wehrhahn, Australia
  • Dr James Robinson, Department of Microbiology and Infectious Diseases, Royal Perth Hospital and PathWest Laboratory Medicine WA, Perth, Australia
  • Mr Patrick Salvaris, Faculty of Medicine and Dentistry, University of Western Australia., Australia
  • Mr Ross Salvaris, Faculty of Medicine and Dentistry, University of Western Australia., Australia
  • Mr David New, Faculty of Medicine and Dentistry, University of Western Australia., Australia
  • Dr Ronan Murray, Department of Microbiology and Infectious Diseases, Royal Perth Hospital and PathWest Laboratory Medicine WA, Perth, Australia

    • Objective: To determine whether the clinical features of invasive community-onset methicillin-resistant Staphylococcus aureus (cMRSA) infection differ from those with methicillin-susceptible S. aureus (cMSSA).

    Methods: Patients with invasive cMRSA infection were identified prospectively at two tertiary hospitals in Western Australia from April 2006 to April 2008. Two contemporaneous cMSSA cases acted as controls. Data was obtained from medical records and laboratory databases.

    Results: Analysis was performed on 150 patients (50 cMRSA and 100 cMSSA). Demographics were similar between the two groups with respect to age and gender; indigenous Australians were over-represented in the cMRSA group (28% vs. 12%, p=0.015). Risk factors such as diabetes (28% vs 25%), intravenous drug use (22% vs 21%) and residential care/hospitalisation in previous 12 months (50% vs 33%) were not significantly different between the cMRSA vs cMSSA groups. Presenting symptoms were similar in each group. Clinical syndromes and sites of infection were also similar, with 74% having skin/soft tissue infection or bone/joint infection in both groups. In cMRSA patients compared with cMSSA patients, 18% vs 12% presented with community acquired pneumonia, while, 2% vs 11% presented with infective endocarditis. Bacteraemia was present in 26% of the cMRSA group and 41% of the cMSSA group. Severity of illness at presentation (as estimated by SAPS II score, and requirement for intensive care support) and length of stay was not significantly different between the two groups. An invasive procedure was performed in 70% and 76% of the cMRSA and cMSSA group respectively. Initiation of effective treatment was delayed in the cMRSA group (61hrs vs. 4hrs, p<0.001). Thirty-day all-cause mortality was similar in the cMRSA and cMSSA groups (10% vs. 7% p = 0.523) however there was a non-significant trend towards increased 30-day mortality in patients with cMRSA bacteraemia compared to those with cMSSA bacteraemia (31% vs. 12%, p=0.117).

    Conclusion: Indigenous Australians bore a disproportionate burden of invasive cMRSA in this study, which reflects the epidemiology of cMRSA colonisation / infection in our region. Neither presenting symptoms, risk factors, nor type of infection differentiated invasive cMRSA infection from that caused by cMSSA. In addition, illness severity and outcomes were similar. As expected, effective therapy was delayed in the cMRSA group, which may in part explain why there was a trend to higher 30-day mortality, particularly in those with bacteraemia.