Abstract
BackgroundAccurate estimates of the incidence and prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections are needed to inform public health policies. In Norway, where both MRSA infection and carriage are notifiable conditions, the reported incidence of MRSA is slowly increasing. However, the proportion of MRSA in relation to all S. aureus isolates is unknown, making it difficult to determine if the rising incidence is real or an artifact of an increasing number of tests performed.AimTo characterize recent trends in MRSA infections and obtain a more complete understanding of the MRSA level in Norway.MethodsAll reported cases of MRSA and methicillin-sensitive S. aureus (MSSA) from Oslo County (1997–2010) and Health Region East (2008–2008), representing approximately 11% and 36% of the Norwegian population, respectively, were analyzed using a stochastic time series analysis to characterize trends.ResultsIn Oslo County, the proportion of methicillin-resistant cases increased from 0.73% to 3.78% during the study period and was well modeled by an exponential growth with a doubling constant of 5.7 years (95% CI 4.5–7.4 years). In Health Region East, the proportion of MRSA cases increased from 0.4% to 2.1% from 2002 to 2008, with a best-fitting linear increase of 0.26% (95% CI 0.21–0.30%) per year. In both cases, the choice of a linear or exponential model for the time trend produced only marginally different model fits. We found no significant changes due to revised national MRSA guidelines published in June 2009. Significant variations in the increasing time trend were observed in the five hospitals within the region. The yearly reported incidence of MSSA was relatively stable in both study areas although we found seasonal patterns with peaks in August.ConclusionThe level of MRSA is increasing in Norway, and the proportion of methicillin resistance in all S. aureus isolates are higher than the reported proportion of MRSA in invasive infections.
Highlights
Over the past six decades, bacterial populations have developed resistance to all commercially available agents, and the emergence of antibiotic resistance is considered to be one of the most important threats to human health in the 21st century [1]
The yearly reported incidence of methicillin-sensitive S. aureus (MSSA) was relatively stable in both study areas we found seasonal patterns with peaks in August
The level of methicillin-resistant Staphylococcus aureus (MRSA) is increasing in Norway, and the proportion of methicillin resistance in all S. aureus isolates are higher than the reported proportion of MRSA in invasive infections
Summary
Over the past six decades, bacterial populations have developed resistance to all commercially available agents, and the emergence of antibiotic resistance is considered to be one of the most important threats to human health in the 21st century [1]. In addition to other Nordic countries and the Netherlands, has managed to keep the prevalence of MRSA low. Both MRSA infection and carriage are notifiable conditions in Norway. While the number and proportion of MRSA in invasive S. aureus infections have been stable at approximately 20 yearly cases and ,1%, respectively, the incidence of MRSA isolates has increased in recent years, both in the community and in healthcare settings [7]. Accurate estimates of the incidence and prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections are needed to inform public health policies. The proportion of MRSA in relation to all S. aureus isolates is unknown, making it difficult to determine if the rising incidence is real or an artifact of an increasing number of tests performed
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