Evolution of mortality over time: results from the COVID-19 Swiss hospital surveillance system (CH-SUR)

Introduction: The assessment of COVID-19 associated mortality is crucial to evaluate the impact of the pandemic and to assess the effectiveness of measures. Objectives: We aimed to investigate trends in COVID-19 related mortality over time in Switzerland, using data from the COVID-19 Hospitalbased Surveillance (CH-SUR) database. Methods: Considering four different time periods of COVID-19 epidemic, we calculated crude and adjusted mortality rates and performed competing risks survival analyses for all patients and for patients admitted to intensive care (ICU). Results: Overall, 16,967 COVID-19 related hospitalizations and 2,307 deaths of adult patients were recorded. Crude hospital mortality rates were 15.6% in the 1st and 14.4% in the 2nd wave;for ICU patients it was 24% and 31.3%, respectively. The overall adjusted risk of death was lower for hospitalised patients during the 2nd compared to the 1st wave (HR 0.75, 95% CI 0.73 - 0.77). In contrast, patients admitted to ICU as well as patients with invasive ventilation presented a higher risk of death during the 2nd wave (HR 1.62, 95% CI 1.54-1.70 and HR 2.10, 95% CI 1.99-2.20, respectively). Conclusion: Our findings may be explained by various changes in the COVID-19 patient management in Swiss hospitals, e.g. with the use of effective drugs against complications or with different guidelines for ICU admission and invasive ventilation use.