title: What is community-associated methicillin-resistant Staphylococcus aureus?
abstract: BACKGROUND
  A community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection has been defined as an MRSA infection in a patient who lacks specific risk factors for healthcare exposure. We sought to determine whether the absence or presence of these risk factors still predicts the phenotypic or genotypic characteristics of MRSA strains.
  
  
  METHODS
  All clinical MRSA isolates were prospectively collected at the University of Chicago Hospitals from July 2004 through June 2005. Patients were interviewed and/or their medical records were reviewed. Isolates underwent genotyping and susceptibility testing. Data on patients and isolates were stratified in accordance with 8 frequently cited criteria for the identification of CA-MRSA and compared for concordance.
  
  
  RESULTS
  Among 616 unique patients from whom MRSA isolates were recovered, 404 (65.6%) had risk factors for healthcare exposure. Of the 404 isolates recovered from these patients, 166 (41.1%) were clindamycin susceptible, 190 (47.0%) carried staphylococcal cassette chromosome mec (SCCmec) type IV, 145 (35.9%) carried the Panton-Valentine leukocidin genes (PVL+), and 162 (40.1%) were identified as sequence type (ST) 8 by multilocus sequence typing (MLST), all of which are characteristics commonly attributed to CA-MRSA strains.
  
  
  CONCLUSIONS
  Association with the healthcare environment now has little predictive value for distinguishing patients with infection due to multidrug resistant MRSA isolates from those infected by CA-MRSA isolates, that is, isolates that are clindamycin-susceptible, PVL+, ST8, and/or contain SCCmec type IV. Defining CA-MRSA by the absence of risk factors for healthcare exposure greatly underestimates the burden of epidemic CA-MRSA disease.
authors.affiliation: Infectious Diseases Section, Department of Pediatrics, the University of Chicago, IL 60637, USA. mdavid@medicine.bsd.uchicago.edu
authors.forename: Michael Z
authors.initials: MZ
authors.lastname: David
authors.forename: Daniel
authors.initials: D
authors.lastname: Glikman
authors.forename: Susan E
authors.initials: SE
authors.lastname: Crawford
authors.forename: Jie
authors.initials: J
authors.lastname: Peng
authors.forename: Kimberly J
authors.initials: KJ
authors.lastname: King
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hostetler
authors.forename: Susan
authors.initials: S
authors.lastname: Boyle-Vavra
authors.forename: Robert S
authors.initials: RS
authors.lastname: Daum
mesh_terms: D017714:Community-Acquired Infections / Q000382:microbiology; D003428:Cross Infection / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics; D006801:Humans; D016106:Methicillin Resistance / Q000235:genetics; D011446:Prospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D004269:DNA, Bacterial