title: Importance of bacterial burden among methicillin-resistant Staphylococcus aureus carriers in a long-term care facility.
abstract: OBJECTIVE
  To evaluate the prevalence and transmission of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization, as well as risk factors associated with MRSA carriage, among residents of a long-term care facility (LTCF).
  
  
  METHODS
  Prospective, longitudinal cohort study.
  
  
  METHODS
  A 100-bed Veterans Administration LTCF.
  
  
  METHODS
  All current and newly admitted residents of the LTCF during an 8-week study period.
  
  
  METHODS
  Nasal swab samples were obtained weekly and cultured on MRSA-selective media, and the cultures were graded for growth on a semiquantitative scale from 0 (no growth) to 6 (heavy growth). Epidemiologic data for the periods before and during the study were collected to assess risk factors for MRSA carriage.
  
  
  RESULTS
  Of 83 LTCF residents, 49 (59%) had 1 or more nasal swab cultures that were positive for MRSA; 34 (41%) were consistently culture-negative (designated "noncarriers"). Of the 49 culture-positive residents, 30 (36% of the total of 83 residents) had all cultures positive for MRSA (designated "persistent carriers"), and 19 (23% of the 83 residents) had at least 1 culture, but not all cultures, positive for MRSA (designated "intermittent carriers"). Multivariate analysis showed that participants with at least 1 nasal swab culture positive for MRSA were likely to have had previous hospitalization (odds ratio, 3.9) or wounds (odds ratio, 8.2). Persistent carriers and intermittent carriers did not differ in epidemiologic characteristics but did differ in mean MRSA growth score (3.7 vs 0.7; P<.001).
  
  
  CONCLUSIONS
  Epidemiologic characteristics differed between noncarriers and subjects with at least 1 nasal swab culture positive for MRSA. However, in this LTCF population, only the degree of bacterial colonization (as reflected by mean MRSA growth score) distinguished persistent carriers from intermittent carriers. Understanding the burden of colonization may be important when determining future surveillance and control strategies.
authors.affiliation: Emory University School of Medicine, Emory University, Atlanta, Georgia, USA. nstone@emory.edu
authors.forename: Nimalie D
authors.initials: ND
authors.lastname: Stone
authors.forename: Donna R
authors.initials: DR
authors.lastname: Lewis
authors.forename: H K
authors.initials: HK
authors.lastname: Lowery
authors.forename: Lyndsey A
authors.initials: LA
authors.lastname: Darrow
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Kroll
authors.forename: Robert P
authors.initials: RP
authors.lastname: Gaynes
authors.forename: John A
authors.initials: JA
authors.lastname: Jernigan
authors.forename: John E
authors.initials: JE
authors.lastname: McGowan
authors.forename: Fred C
authors.initials: FC
authors.lastname: Tenover
authors.forename: Chesley L
authors.initials: CL
authors.lastname: Richards
mesh_terms: D002353:Carrier State; D015331:Cohort Studies; D003428:Cross Infection; D006801:Humans; D008134:Long-Term Care; D008137:Longitudinal Studies; D016106:Methicillin Resistance; D009735:Nursing Homes; D015995:Prevalence; D011446:Prospective Studies; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000635:transmission*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification / Q000472:pathogenicity*