Changing epidemiology of methicillin-resistant Staphylococcus aureus in Finland.

Data on methicillin-resistant Staphylococcus aureus (MRSA) cases notified to the National Infectious Disease Register (NIDR) and antibiotic resistance profiles of MRSA isolates sent to the national reference laboratory between 1997 and 2002 were analysed. In addition, the diagnostic methods used for MRSA identification in Finnish microbiology laboratories, the number of MRSA screening specimens studied, and the MRSA situation in long-term care facilities in 2001 were reviewed. MRSA cases notified to the NIDR rose from 120 in 1997 to 597 in 2002 (from 2.3 to 11.5 cases per 100,000 population). The increase was greatest in elderly people and outside Helsinki metropolitan area, in the districts where the proportion of non-multiresistant strains was most prominent. The National Committee for Clinical Laboratory Standard's guidelines for the oxacillin disk diffusion test were followed, except for the incubation temperature and time, which may have hindered detection of some MRSA strains. There was a wide geographic variation in the rates of MRSA, but this was not related to screening activity. MRSA isolates from long-term facilities accounted for more than half of the notifications to the NIDR in 2001.