Increase in Methicillin-susceptible Staphylococcus Aureus Bloodstream Infections in Switzerland: a Nationwide Surveillance Study (2008-2021)

Purpose: An increasing burden of Staphylococcus aureus bloodstream infections (BSI), despite a decrease in the percentage of methicillin-resistant S. aureus (MRSA), was described recently in other European countries. The main aim of this study was to analyse recent temporal trends of S. aureus, methicillin-susceptible S. aureus (MSSA) and MRSA BSI for Switzerland as well as the different linguistic regions within Switzerland. An additional aim was to estimate potential differences among patient-based and epidemiological risk factors.

Methods: A retrospective observational study was conducted in Switzerland over a period of 14 years (2008-2021). Trends in S. aureus, MSSA and MRSA BSI were analysed by applying linear regression models.

Results: Staphylococcus aureus BSI increased by + 30% from 19.7 to 25.6 cases per 100,000 inhabitants between 2008 and 2021 (P < 0.01) in Switzerland. Thereof, MSSA increased by + 37% from 17.8 to 24.4 cases per 100,000 inhabitants (P < 0.01). MRSA decreased from 1.9 to 1.2 cases per 100,000 inhabitants (P < 0.01), which was driven by decreasing incidence in the French-speaking region. MSSA BSI increased significantly (P < 0.01) in both linguistic regions. A further stratification revealed that incidence increased the most in male patients of the age group ≥ 80 years of the German-speaking region.

Conclusion: The increasing health burden of MSSA BSI in Switzerland indicates that not only proportions of resistant microorganisms but also total BSI incidences should be monitored. In addition, data stratification revealed that the increase was mainly driven by an increasing incidence in elderly males of the German-speaking region.