title: MRSA nasal colonization burden and risk of MRSA infection.
abstract: BACKGROUND
  Staphylococcus aureus nasal colonization burden has been identified as a risk factor for infection. This study evaluates methicillin-resistant S aureus (MRSA) nasal burden, as defined by the cycle threshold (Ct) and risk of subsequent infection.
  
  
  METHODS
  In a retrospective cohort study, United States veterans were classified into 3 MRSA nasal colonization groups: noncarriers, low burden (Ct > 24 cycles), and high burden (Ct ≤ 24 cycles). MRSA infections were identified prospectively, and clinical information was obtained by chart review. Multivariate logistic regression assessed the association of MRSA nasal burden and risk of MRSA infection.
  
  
  RESULTS
  During 4-years of follow-up, 4.3% of noncarriers, 18.5% of low burden, and 17.2% of high burden developed a MRSA infection. In multivariate analysis, MRSA nasal colonization was a risk factor for MRSA infection (P = .008) with low burden (risk ratio [RR], 3.62; 95% confidence interval [CI]: 1.47-8.93) and high burden (RR, 2.71; 95% CI: 0.95-7.72) associated with subsequent MRSA infection when compared with noncarriers. When compared with low burden, high burden nasal carriers were not at increased risk of infection (RR, 0.75; 95% CI 0.36-1.55).
  
  
  CONCLUSIONS
  MRSA nasal colonization was a risk factor for MRSA infection. High nasal burden of MRSA did not increase the risk of infection.
authors.affiliation: Atlanta Veterans Affairs Medical Center, Decatur, GA, USA. eddie.stenehjem@imail.org
authors.forename: Edward
authors.initials: E
authors.lastname: Stenehjem
authors.forename: David
authors.initials: D
authors.lastname: Rimland
mesh_terms: D000368:Aged; D058345:Asymptomatic Infections / Q000453:epidemiology*; D058491:Bacterial Load; D002353:Carrier State / Q000453:epidemiology*; D015331:Cohort Studies; D003428:Cross Infection / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000254:growth & development*; D008875:Middle Aged; D009296:Nasal Cavity / Q000382:microbiology*; D012008:Recurrence; D012189:Retrospective Studies; D012306:Risk; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology / Q000401:mortality / Q000635:transmission