Unusual spread of a penicillin-susceptible methicillin-resistant Staphylococcus aureus clone in a geographic area of low incidence

We describe the unusual spread of a penicillin-susceptible methicillin-resi stant Staphylococcus aureus (MRSA) clone in hospitals in western Switzerlan d, where the incidence of MRSA is usually low. During a 2-year period, this clone had been responsible for several outbreaks and had been isolated fro m >156 persons in 21 institutions. Molecular typing by pulsed-field gel ele ctrophoresis (PFGE) demonstrated that all of these isolates belonged to he same clone. In 1 of the outbreaks, involving 30 cases, the clone was respon sible for at least 17 secondary cases. In contrast, during the period of th e latter outbreak, 9 other patients harboring different MRSA strains, as as sessed by PFGE, were hospitalized in the same wards, but no secondary cases occurred. These observations suggest that this clone, compared with other MRSA strains, had some intrinsic factor(s) that contributed to its ability to disseminate and could thus be considered epidemic.