Epidemiology of Staphylococcus aureus nasal colonization and influence on outcome in the critically ill.

PURPOSE: To determine the rate of Staphylococcus aureus nasal colonization at admission to intensive care units (ICU) and assess its effect on the development of an ICU-acquired S aureus infection.

MATERIALS AND METHODS: We screened all ICU admissions for nasal colonization within the Calgary Health Region from October 2005 to September 2006 and followed up patients to hospital discharge or death or S aureus infection to 30 days.

RESULTS: One thousand three hundred eight patients were admitted to ICU for more than 48 hours and screened for nasal colonization. Fifty (4%) were methicillin-resistant S aureus (MRSA)-positive, 311 (24%) were methicillin-sensitive S aureus (MSSA)-positive, and 947 (72%) were nasal screen-negative. Overall, 5% (63/1239) of patients uninfected at ICU admission developed an ICU-acquired S aureus infection. The rate of ICU-acquired infection was 5% in MRSA colonized patients, 12% in MSSA colonized patients, and 3% in noncolonized patients. A positive nasal screen (odds ratio [OR], 4.7; 95% confidence interval [CI] 2.7-7.9), neuro/trauma patients (OR, 3.1; 95% CI, 1.8-5.2), and higher first Therapeutic Intervention Scoring System score (OR, 1.03 per point; 95% CI, 1.01-1.05) were independent predictors for developing an ICU-acquired S aureus infection.

CONCLUSIONS: Nasal colonization with S aureus is a significant risk factor for ICU-acquired S aureus infections, and strategies to control these infections should target both MSSA and MRSA colonization.