Staphylococcus Aureus Nasal Colonization in the United States: Analysis of Risk and Protective Factors from the National Health and Nutrition Examination Survey, 2001-2004

Background: Staphylococcus-aureus (SA) and Methicillin-resistant-SA (MRSA) are increasingly found outside of hospitals and in community settings. We examined risk and protective factors of nasal-colonization with SA and MRSA in a population-based dataset.

Methods: We used data from 2001-2004 National Health and Nutritional Examination Survey, a representative survey of US non-institutionalized civilian population, to determine prevalence, and risk, and protective factors for nasal-colonization with SA and MRSA. We utilized information on nasal-colonization status with SA, MRSA, Staphylococcal cassette chromosome (SCCmec) type/subtypes, and socio-demographics (age, gender, race/ethnicity, marital status, smoking status, secondhand-smoke-exposure (SHS), poverty-index). We calculated odds-ratios (OR) with 95% confidence intervals (95%CI) from multivariate logistic regression models, accounting for the complex sampling design.

Results: SA nasal-colonization prevalence decreased from 32.4% (2001-2002) to 28.6% (2003-2004). Being divorced/separated/widowed (OR=1.32; 95%CI=1.1-1.59) was a risk factor; increased age (OR=0.99; 95%CI=0.98-0.99), females (OR=0.65; 95%CI=0.55-0.75), non-Hispanic-Blacks (OR=0.62; 95%CI=0.52-0.74) and current-smokers (OR=0.71; 95%CI=0.62-0.80) were protected from SA colonization. MRSA nasal-colonization prevalence increased from 2.6% (2001-2002) to 5.2% (2003-2004). The majority of MRSA isolates had Type-II-SCCmec (51%) while 49% had Type-IV-SCCmec. Significant risk factors for MRSA nasal-colonization included increasing age (OR=1.03; 95%CI=1.01-1.06), being female (OR=2.37; 95%CI=1.41-3.98), and former smokers (OR=3.12; 95%CI=1.44-6.79).

Discussion: SA nasal-colonization shows a reversed pattern of risk and protective factors from that of MRSA. Prevalence of MRSA has increased while SA nasal-colonization has decreased. Moreover, increased prevalence of type-II-SCCmec in community-based settings may reflect an alarming propagation trend of this primarily hospital-acquired infection. Future research should investigate methods to contain this potentially devastating public health burden.