Daily hazard of MRSA acquisition in the intensive care unit

  • Caroline Marshall, The Royal Melbourne Hospital and University of Melbourne, Australia
  • Associate Professor D Spelman, The Alfred Hospital, Australia
  • Ms Glenys Harrington, The Alfred Hospital, Australia
  • Dr Emma McBryde, The Royal Melbourne Hospital, Australia

    • Objective: Increasing length of hospital stay is associated with methicillin-resistant Staphylococcus aureus (MRSA) acquisition. The exact risk of becoming colonised with MRSA on a given day has not been clearly elucidated. We determined the hazard of MRSA acquisition against length of time spent in the intensive care unit.
    Methods: This study took place at a tertiary referral hospital intensive care unit where patients were screened for MRSA on admission, discharge and twice weekly. We analysed the hazard of MRSA acquisition against length of time spent in ICU using an Epanechnikov kernel for hazard smoothing with a width of 5 days.
    Results: 12.4% of at risk patients acquired MRSA. The average length of ICU stay was 7.2 days. The daily hazard of acquiring MRSA increased linearly to nearly 4% risk per day by day 21, followed by a leveling out of risk.
    Conclusion: The daily hazard of acquiring MRSA is not constant. This has implications for studies that assume a constant hazard in their analysis and should be taken into account.