title: Daily hazard of acquisition of methicillin-resistant Staphylococcus aureus infection in the intensive care unit.
abstract: OBJECTIVE
  Increasing length of hospital stay is associated with methicillin-resistant Staphylococcus aureus (MRSA) acquisition. The exact risk of becoming colonized with MRSA on a given day has not been clearly elucidated. We determined the hazard of MRSA acquisition in relation to the length of time spent in an intensive care unit in which only standard precautions were used for MRSA-colonized and MRSA-infected patients.
  
  
  METHODS
  This study took place at a tertiary referral hospital intensive care unit in which patients were screened for MRSA at hospital admission, at hospital discharge, and twice weekly during intensive care unit stay. We analyzed the hazard of MRSA acquisition by using a statistical smoothing kernel for hazard with a width of 5 days. Patients were stratified according to age, sex, medical unit, and length of hospital stay.
  
  
  RESULTS
  Of the patients who were at risk of colonization or infection, 12.8% acquired MRSA. The mean length of stay in the intensive care unit was 7.2 days. The daily hazard of acquiring MRSA was less than 1% at admission to the intensive care unit and increased linearly to more than 2% risk per day by day 12, followed by a leveling out of risk.
  
  
  CONCLUSIONS
  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 considered.
authors.affiliation: Centre for Clinical Research Excellence in Infectious Diseases, University of Melbourne, Melbourne, Australia. caroline.marshall@mh.org.au
authors.forename: Caroline
authors.initials: C
authors.lastname: Marshall
authors.forename: Denis
authors.initials: D
authors.lastname: Spelman
authors.forename: Glenys
authors.initials: G
authors.lastname: Harrington
authors.forename: Emma
authors.initials: E
authors.lastname: McBryde
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002353:Carrier State / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology / Q000635:transmission; D003428:Cross Infection / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology / Q000635:transmission*; D005260:Female; D006801:Humans; D007362:Intensive Care Units / Q000706:statistics & numerical data*; D007902:Length of Stay / Q000706:statistics & numerical data*; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000302:isolation & purification; D008875:Middle Aged; D018570:Risk Assessment; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology / Q000635:transmission*; D055815:Young Adult