Emergence and dissemination of the methicillin resistant Staphylococcus aureus USA300 clone in Denmark (2000-2005)

The problem of methicillin resistant Staphylococcus aureus (MRSA) is increasing worldwide, and the spread of MRSA in the community challenges infection control since it is no longer restricted to hospital settings but involves private homes, places of work and kindergartens [1]. Furthermore, community acquired (CA)-MRSA may circumvent existing hospital infection control, since patients are rarely screened at admission. In the United States, the predominant CA-MRSA is defined by the Center for Disease Control (CDC) as the USA300 (ST8) clone. USA300 primarily causes skin and soft tissue infections (SSTI) in the community [2], but healthcare acquired infections with USA300 are rapidly emerging in the United States [3,4]. Comparison of the Danish collection of MRSA from 1997-2005 with the USA300 reference strain showed that USA300 has been introduced into Denmark on several occasions. Between 2000 and 2005, we identified 44 isolates which in addition to identical pulsed-field gel electrophoresis (PFGE) pattern shared other molecular characteristics with USA300: spa type t008 or closely related variants, Panton-Valentine leukocidin (PVL) positive and Staphylococcal Cassette Chromosome mec (SCCmec) type IVa. The isolates primarily caused SSTI, but cases of invasive infections were also encountered. The number of USA300 has increased several-folds in Denmark from 2003 to 2005 (2, 11 and 28 new cases, respectively) and with the experience from the US in mind, this is of great concern, especially as it is observed in a country with a long reputation for controlling MRSA.