The epidemiology and genetic structure of Staphylococcus aureus populations causing invasive disease in Auckland, New Zealand

  • Stephen Ritchie, University of Auckland, New Zealand
  • Prof John Fraser, University of Auckland, New Zealand
  • Dr David Holland, Middlemore Hospital, New Zealand
  • Prof Paul Rainey, New Zealand Institute for Advanced Study, Massey University, New Zealand
  • Dr Sally Roberts, LabPLUS, Auckland City Hospital, New Zealand
  • A/Prof Mark Thomas, University of Auckland, New Zealand

    • The overall incidence of invasive SA disease in Auckland NZ is approximately 1:2500 and is higher in Maori and Pacific people with a crude mortality rate of 19%.
    Objective:To describe the epidemiology of cases of SA bacteraemia and to describe the genetic structure of SA populations in Auckland.
    Methods:Adult inpatients with SA bacteraemia were recruited between March 2007 and March 2008. Participants completed a questionairre regarding their health, exposure to SA and their social demography. Each blood culture isolate was strain typed by MLST. Strains of SA isolated from nasal swabs from healthy subjects with no recent hospital contact were also strain typed for comparison.
    Results:162 cases of SA bacteraemia were identified and 153 consented to participate in the study. A high proportion of cases had healthcare associated infection (71%), commonly due to infection of a vascular device (43%). Almost all participants (93%) had a regular GP, however some (18%) did not have access to a telephone or cell-phone and just over half were able to heat their homes in winter. A quarter died as a consequence of their infection.
    The MLST data from the bacteraemic and community isolates will be examined for evidence of healthcare associated vs. community, geographic, and ethnic clustering.
    Conclusion:It is of utmost importance that the epidemiology and ecology of this infection is understood so that preventative measures can be investigated.