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

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.

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.

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.

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.