title: Models to predict prevalence and transition dynamics of methicillin-resistant Staphylococcus aureus in community nursing homes.
abstract: Recent spread of USA300 methicillin-resistant Staphylococcus aureus (MRSA) to nursing homes has been of particular concern. We sought to predict the ultimate prevalence of USA300 and non-USA300 MRSA and to examine the influence of potential risk factors on MRSA acquisition in community nursing homes.
  
  
  
  The data were collected during a longitudinal MRSA surveillance study that involved 449 residents in 6 community nursing homes in Wisconsin. The subjects were screened every 3 months for up to 1 year. Markov chain models were employed to predict strain-specific prevalence of MRSA at steady state, and to assess the influence of potential risk factors, including recent hospitalizations, invasive medical devices, and antibiotic exposure on MRSA acquisition rates and average duration of colonization.
  
  
  
  At steady state, 20% (95% confidence interval [CI], 15%-25%) of residents were predicted to remain colonized with non-USA300 and 4% (95% CI, 2%-7%) with USA300 MRSA. Residents who used antibiotics during the previous 3 months were twice more likely to acquire MRSA than those who did not (acquisition rates, 0.052; 95% CI, 0.038-0.075 and 0.025; 95% CI, 0.018-0.037, respectively).
  
  
  
  Non-USA300 was predicted to remain the dominant MRSA strain in community nursing homes. The higher rate of MRSA acquisition among residents with recent antibiotic exposure suggests that antibiotic stewardship may reduce MRSA colonization in this setting.
authors.affiliation: Department of Industrial and Systems Engineering, University of Wisconsin-Madison, Madison, WI. Electronic address: ngbatina@gmail.com.
authors.forename: Nataliya G
authors.initials: NG
authors.lastname: Batina
authors.affiliation: Department of Industrial and Systems Engineering, University of Wisconsin-Madison, Madison, WI; Department of Medicine, University of Wisconsin-Madison, Madison, WI; William S. Middleton Veterans Affairs Hospital, Madison, WI.
authors.forename: Christoper J
authors.initials: CJ
authors.lastname: Crnich
authors.affiliation: Department of Mathematics, University of Wisconsin-Madison, Madison, WI.
authors.forename: David F
authors.initials: DF
authors.lastname: Anderson
authors.affiliation: Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI; Department of Population Health Sciences, University of Wisconsin-Madison, Madison, WI.
authors.forename: Dörte
authors.initials: D
authors.lastname: Döpfer
mesh_terms: D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology*; D006801:Humans; D008137:Longitudinal Studies; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D009735:Nursing Homes; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D014922:Wisconsin
keywords: USA300 MRSA; acquisition rates; colonization; non-USA300 MRSA; prevalence; risk factors