title: Molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization and infection isolates in a Veterans Affairs hospital.
abstract: BACKGROUND
  Nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) is associated with increased infection risk, yet colonization and infection isolates are rarely compared within the same study. The objectives of this study were to compare colonization and infection isolates from a Veterans Administration hospital in Iowa, and to determine the prevalence of livestock-associated MRSA (LA-MRSA) colonization and infection in a state with high livestock density.
  
  
  METHODS
  All patients with available MRSA isolates collected through routine nasal screening (73%; n = 397) and from infections (27%; n = 148) between December 2010 and August 2012 were included and tested for spa type and presence of PVL and mecA genes. Clinical isolates were tested for antibiotic resistance patterns. Paired colonization and infection isolates were compared for genetic and phenotypic congruity.
  
  
  RESULTS
  The most common spa types were t002 (and other CC5-associated strains; 65%) and t008 (and other CC8-associated strains; 20%). No classic LA-MRSA spa types were identified. CC5-associated strains were less likely to be associated with infections (22%; 77/353) compared with CC8-associated strains (49%; 53/109). MRSA colonization was more common among patients with infections (71%) compared with the general screening population (7%). In most cases (82%; 28/34), paired colonization and infection isolates were genetically and phenotypically indistinguishable.
  
  
  CONCLUSIONS
  Our data demonstrate a direct link between antecedent nasal colonization and subsequent MRSA infection. Further, our data indicate variability in colonization and infection efficiency among MRSA genotypes, which points to the need to define the molecular determinants underlying emergence of S. aureus strains in the community and nosocomial setting.
authors.affiliation: Department of Epidemiology, University of Iowa College of Public Health, Iowa City, IA 52246 USA.
authors.forename: Kalyani E
authors.initials: KE
authors.lastname: Eko
authors.affiliation: Department of Epidemiology, University of Iowa College of Public Health, Iowa City, IA 52246 USA.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Forshey
authors.affiliation: Department of Epidemiology, University of Iowa College of Public Health, Iowa City, IA 52246 USA ; Department of Geographical & Sustainability Sciences, University of Iowa, Iowa City, IA 52242 USA.
authors.forename: Margaret
authors.initials: M
authors.lastname: Carrel
authors.affiliation: Center for Comprehensive Access & Delivery Research and Evaluation (CADRE), Iowa City VA Health Care System, Iowa City, IA 52246 USA ; Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA 52246 USA.
authors.forename: Marin L
authors.initials: ML
authors.lastname: Schweizer
authors.affiliation: Center for Comprehensive Access & Delivery Research and Evaluation (CADRE), Iowa City VA Health Care System, Iowa City, IA 52246 USA ; Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA 52246 USA.
authors.forename: Eli N
authors.initials: EN
authors.lastname: Perencevich
authors.affiliation: Department of Epidemiology, University of Iowa College of Public Health, Iowa City, IA 52246 USA ; Department of Biostatistics, Environmental Health Sciences and Epidemiology, College of Public Health, Kent State University, Kent, OH 44242 USA.
authors.forename: Tara C
authors.initials: TC
authors.lastname: Smith
keywords: Hospital acquired infections; Infection control; MRSA; Staphylococcus aureus
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