Objective
Surveillance of Staphylococcus aureus bacteraemia (SAB) and MRSA has been performed at Statens Serum Institute (SSI) since 1957. From 2007, spa-typing has been the primary typing method. In this investigation we compare the distri-bution of clonal complexes (CCs) among bacteraemia isolates of methicillin sen-sitive S. aureus (MSSA) and methicillin resistant S. aureus (MRSA).

Methods
The majority of isolates (1011/1364 of bacteraemia, and all MRSA isolates (n=659)) received at SSI in 2007 were spa-typed and consecutively annotated to a clonal complex (CC) based on relatedness to spa-types with known MLST types.

Results
The bacteraemia isolates belonged to 379 different spa-types, and could be an-notated to 23 known CCs. Ninety isolates (60 spa-types) could not be annotated to a CC. CC45 (24%) was the largest group among the bacteraemia isolates, fol-lowed by CC30 (14%), CC15 (12%), CC8 (7%) and CC5 (7%). CC45 was a large and heterogeneous group consisting of more than 60 different spa-types. The MRSA isolates belonged to 111 different spa-types, and could be annotated to 18 known CCs. For the MRSA, CC8 (31%) was the largest group, followed by CC5 (16%), CC22 (10%), CC80 (10%) and CC30 (8%). Only 0.5% of the bacteraemia isolates were MRSA. Several bacteraemia CC groups were not commonly found among MRSA, such as CC15, CC12, and CC20. CC15 constituted 12% of the spa-typed bacteraemia isolates, but only six MRSA isolates belonging to CC15 has been found in Denmark since 2004. The only major MRSA CC group not found among the bacteraemias was CC80. In 2007, 11% of the new MRSA cases were CC80.

Conclusion
Spa-typing of a large number of bacteraemia isolates confirms that MSSA is a much more heterogeneous group than MRSA, with greater variation in spa types and CC groups.