NOSOCOMIAL STAPHYLOCOCCUS-AUREUS BACTEREMIA AMONG NASAL CARRIERS OF METHICILLIN-RESISTANT AND METHICILLIN-SUSCEPTIBLE STRAINS

OBJECTIVES: TO determine the relevance of nasal carriage of Staphyloco ccus aureus, either methicillin-sensitive (MSSA) or methicillin-resist ant (MRSA), as a risk factor for the development of nosocomial S aureu s bacteremia during an MRSA outbreak. PATIENTS AND METHODS: In this pr ospective cohort study, 488 patients admitted to an intensive cave uni t (ICU) during a 1-year period were screened with nasal swabs within 4 8 hours of admission and weekly thereafter in order to identify nasal S aureus carriage. Nasal staphylococcal carriers were observed until d evelopment of S aureus bacteremia, ICU discharge, or death. RESULTS: O ne hundred forty-seven (30.1%) of 488 patients were nasal S aureus car riers; 84 patients (17.2%) harbored methicillin-sensitive S aureus; an d 63 patients (12.9%) methicillin-resistant S aureus. Nosocomial S aur eus bacteremia was diagnosed in 38 (7.7%) of 488 patients. Rates of ba cteremia were 24 (38%) of the MRSA carriers, eight (9.5%) of the MSSA carriers, and six (1.7%) of noncarriers. After adjusting for other pre dictors of bacteremia by means of a Cox proportional hazard regression model, the relative risk for S aureus bacteremia was 3.9 (95% confide nce interval, 1.6-9.8; P = 0.002) for MRSA carriers compared with MSSA carriers. CONCLUSIONS: Among ICU patients, nasal carriers of S aureus are at higher risk for S aureus bacteremia than are noncarriers; in t he setting of an MRSA outbreak, colonization by methicillin-resistant strains represents a greater risk than does colonization by MRSA and s trongly predicts the occurrence of MRSA bacteremia.