title: Methicillin-resistant Staphylococcus aureus (MRSA) nasal carriage in residents of Veterans Affairs long-term care facilities: role of antimicrobial exposure and MRSA acquisition.
abstract: OBJECTIVE
  To identify risk factors associated with methicillin-resistant Staphylococcus aureus (MRSA) acquisition in long-term care facility (LTCF) residents.
  
  
  METHODS
  Multicenter, prospective cohort followed over 6 months.
  
  
  METHODS
  Three Veterans Affairs (VA) LTCFs.
  
  
  METHODS
  All current and new residents except those with short stay (<2 weeks).
  
  
  METHODS
  MRSA carriage was assessed by serial nares cultures and classified into 3 groups: persistent (all cultures positive), intermittent (at least 1 but not all cultures positive), and noncarrier (no cultures positive). MRSA acquisition was defined by an initial negative culture followed by more than 2 positive cultures with no subsequent negative cultures. Epidemiologic data were collected to identify risk factors, and MRSA isolates were typed by pulsed-field gel electrophoresis (PFGE).
  
  
  RESULTS
  Among 412 residents at 3 LTCFs, overall MRSA prevalence was 58%, with similar distributions of carriage at all 3 facilities: 20% persistent, 39% intermittent, 41% noncarriers. Of 254 residents with an initial negative swab, 25 (10%) acquired MRSA over the 6 months; rates were similar at all 3 LTCFs, with no clusters evident. Multivariable analysis demonstrated that receipt of systemic antimicrobials during the study was the only significant risk factor for MRSA acquisition (odds ratio, 7.8 [95% confidence interval, 2.1-28.6]; P = .002). MRSA strains from acquisitions were related by PFGE to those from a roommate in 9/25 (36%) cases; 6 of these 9 roommate sources were persistent carriers.
  
  
  CONCLUSIONS
  MRSA colonization prevalence was high at 3 separate VA LTCFs. MRSA acquisition was strongly associated with antimicrobial exposure. Roommate sources were often persistent carriers, but transmission from roommates accounted for only approximately one-third of MRSA acquisitions.
authors.affiliation: Emory University School of Medicine, Atlanta, Georgia, USA. nstone@cdc.gov
authors.forename: Nimalie D
authors.initials: ND
authors.lastname: Stone
authors.forename: Donna R
authors.initials: DR
authors.lastname: Lewis
authors.forename: Theodore M
authors.initials: TM
authors.lastname: Johnson
authors.forename: Thomas
authors.initials: T
authors.lastname: Hartney
authors.forename: Doris
authors.initials: D
authors.lastname: Chandler
authors.forename: Johnita
authors.initials: J
authors.lastname: Byrd-Sellers
authors.forename: John E
authors.initials: JE
authors.lastname: McGowan
authors.forename: Fred C
authors.initials: FC
authors.lastname: Tenover
authors.forename: John A
authors.initials: JA
authors.lastname: Jernigan
authors.forename: Robert P
authors.initials: RP
authors.lastname: Gaynes
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000009:adverse effects; D003428:Cross Infection / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology* / Q000635:transmission; D005260:Female; D006787:Hospitals, Veterans; D006801:Humans; D017053:Infection Control; D016015:Logistic Models; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D008875:Middle Aged; D015999:Multivariate Analysis; D009666:Nose / Q000382:microbiology; D015995:Prevalence; D011446:Prospective Studies; D012112:Residential Facilities; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology* / Q000635:transmission
chemical_list: D000900:Anti-Bacterial Agents