USA300 methicillin-resistant Staphylococcus aureus in Zurich, Switzerland between 2001 and 2013

USA300 methicillin-resistant Staphylococcus aureus (MRSA) is the most prevalent MRSA in the United States of America (USA) and a global epidemic threat. We investigated the prevalence of USA300 at a tertiary care hospital in Zurich, Switzerland, where all MRSA strains have been collected and PFGE typed since 1992. These strains were retrospectively compared to the PFGE pattern of USA300 strain JE2. Isolates with a respective PFGE pattern were spa-typed and tested for the presence of the arginine catabolic mobile element (ACME) arc gene cluster and Panton-Valentine Leucocidin (PVL) genes. The first MRSA strain with a USA300 PFGE pattern was isolated in 2001 from a patient visiting from the USA. USA300 strains represented between 0% (in 2002) and 9.2% (in 2012) of all MRSA isolates in our hospital. We identified various USA300 subtypes based on either the PFGE pattern, the spa-type or absence of either the PVL genes or ACME arc gene cluster. All the USA300 strains including the variants (n=47) accounted for 5.6% of all MRSA isolates typed between 2001 and 2013 and reached a maximum of 14.5% in 2009. They predominantly caused skin and soft tissue infections (74.4%). In conclusion, even though USA300 has been present in our hospital for over twelve years it has not become the predominant MRSA clone like in the USA. However, in light of the global burden of USA300, care must be taken to further contain the spread of this lineage and of MRSA in general in our hospital.