MRSA nasal colonization burden and risk of MRSA infection

• Authors: Edward Stenehjem, Emory University; David Rimland, Emory University
• Journal Title: American Journal of Infection Control
• Volume: Volume 41, Number 5
• Publisher: Elsevier: 12 months | 2013-05-01, Pages 405-410
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1016/j.ajic.2012.07.017
• Subjects: Health Sciences, Pathology; Health Sciences, Public Health; Health Sciences, Epidemiology
• Keywords: Science & Technology; Life Sciences & Biomedicine; Public, Environmental & Occupational Health; Infectious Diseases; Staphylococcus aureus; Carriage quantification; Cycle threshold; RESISTANT STAPHYLOCOCCUS-AUREUS; METHICILLIN-RESISTANT; CHANGING EPIDEMIOLOGY; LONG-TERM; CARRIAGE; CARRIERS; PERSISTENT; BACTEREMIA; VETERANS

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). Conclusion: MRSA nasal colonization was a risk factor for MRSA infection. High nasal burden of MRSA did not increase the risk of infection.