Epidemiology and Clonality of Methicillin-Resistant and Methicillin-SusceptibleStaphylococcus aureusCausing Bacteremia in a Tertiary-Care Hospital in Spain

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Abstract
Objectives:: To describe the relative proportions of nosocomial and community-onsetStaphylococcus aureusbacteremia at our institution and the epidemiologic characteristics and clonal diversity ofS. aureusisolates, as determined by pulsed-field gel electrophoresis (PFGE) and antimicrobial resistance patterns.Design:: Retrospective cohort study of all cases ofS. aureusbacteremia between October 2001 and October 2002.Setting:: A 1,300-bed, tertiary-care hospital.Results:: One hundred sixty-two unique episodes ofS. aureusbacteremia were identified. Forty-three cases (26.5%) were caused by methicillin-resistantS. aureus(MRSA). Most cases ofS. aureusbacteremia, whether MRSA or methicillin susceptible (MSSA), were nosocomial in origin (77.2%) or were otherwise associated with the healthcare system (16%). Only 11 (6.8%) of the cases (all MSSA) were strictly community acquired. Thirty-five unique macrorestriction patterns were identified among the 154 isolates that were typed by PFGE. Four major genotypes were defined among the isolates of MRSA, with 36 (85.7%) represented by a single PFGE type. Of the isolates within this major clone, all (100%) were ciprofloxacin resistant and 77.8% were erythromycin resistant. In contrast, the 112 isolates of MSSA comprised 31 different PFGE types, 3 of which represented 42.9% of all MSSA isolates and were associated with both nosocomial and community-onset bacteremia.Conclusions:: Most cases ofS. aureusbacteremia in our healthcare region are nosocomial in origin or are acquired through contact with the healthcare system and are thus potentially preventable. To preclude dissemination of pathogenic clones, it is therefore necessary to redouble preventive measures in both the hospital and the community.

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