Staphylococcus aureus bacteraemia in Iceland, 1995-2008: changing incidence and mortality

Little is known about temporal changes in the epidemiology of Staphylococcus aureus bacteraemia. The objective of the present study was to analyse changes in the incidence and mortality of adult S. aureus bacteraemia in Iceland. Individuals 18 years or older with a positive blood culture for S. aureus between 1 January 1995 and 31 December 2008 were identified, with the participation of all clinical microbiological laboratories performing blood cultures in Iceland. Infections were categorized as nosocomial, healthcare-associated or community-acquired. National population statistics and dates of death were retrieved from the National Registry. During the study period, 692 individuals from 19 institutions had 721 distinct episodes of S. aureus bacteraemia. The incidence rose from 22.7 to 28.9 per 100,000 per year during the period (p 0.012). Nosocomial infections comprised 46.3% of cases, 14.6% were healthcare-associated, and 39.1% were community-acquired. The proportion of nosocomial infections decreased during the period (p <0.001), whereas an increase was seen in the proportion of community-acquired infections (p <0.001). All-cause 30-day mortality decreased from 25.0% to 8.1% (p 0.001) and 1-year mortality decreased from 37.0% to 27.9% (p 0.061) between the periods 1995-1996 and 2007-2008. Four cases of bacteraemia caused by methicillin-resistant S. aureus were seen (0.6%), none of which was fatal. In conclusion, there was a significant increase in the incidence of S. aureus bacteraemia in Iceland between 1995 and 2008. Concomitantly, there was a significant reduction in mortality, towards one of the lowest reported. Further studies are needed to understand the basis for these changes.