| Summary: | Staphylococcus aureus is a major cause of bloodstream infections and endocarditis. S. aureus bacteraemia (SAB) is associated with substantial morbidity and mortality, and endocarditis is a severe complication. Population-based studies on S. aureus bacteraemia have been sparse, and few large studies exist on S. aureus endocarditis (SAE). The objective of this thesis was to study the epidemiology, characteristics, and short- and long-term outcome of S. aureus bacteraemia and endocarditis in Iceland and Stockholm. In paper I and II we studied SAB in the entire Icelandic adult and paediatric populations. Cases were retrospectively identified at the clinical microbiological laboratories. In adults the incidence was 24.5 /100,000 person-years during 1995-2008 (721 cases), increasing by 28% during the study period (p=0.01). The paediatric incidence was 10.9 /100,000 child-years during 1995-2011 (146 cases), decreasing by 36% during the period (p=0.001). At the same time the average annual frequency of blood cultures from children analysed at the main study site decreased by 27% (p<0.001). SAB incidence was highest in infants (<1 year), 58.8 /100,000. The proportion of adults with nosocomial infections decreased from 56% in 1995-99 to 39% in 2005-08 (p=0.001), while community acquired SAB increased from 29% to 46% (p<0.001). Health-care associated community-onset cases were 15%. Among the paediatric cases 34% were nosocomial, 14% health-care associated, and 51% community acquired. Bone or joint infection was the focus of SAB in 40% of children, followed by intravascular catheters in 30%, and an unknown focus in 10%. The 30-day mortality in adults was 17.1%, and decreased from 22.2% during 1995-99 to 11.4% during 2005-08 (p=0.001). The 1-year mortality was 33.0%, and decreased from 38.9% to 28.2% (p=0.06). In children the SAB-related mortality was 0.7%, 30-day mortality 1.4%, and the 1-year mortality 3.6%. These case fatality ratios are lower than those observed in most previous studies. In paper III we studied ...
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