Outcomes of influenza and COVID-19 inpatients in different phases of the SARS-CoV-2 pandemic: a single-centre retrospective case–control study

BACKGROUND: The virulence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) changed during the pandemic. In order to provide a rationale for treatment priorities of respiratory infections and the adaption of in-house infection control strategies, this study evaluated treatment on an intensive care unit (ICU), requirement for mechanical ventilation (MV), requirement for extracorporeal membrane oxygenation (ECMO) and death for inpatients infected with the influenza virus or SARS-CoV-2 during the wild-type, Alpha, Delta, Omicron BA.1/2 and Omicron BA.5 waves of the pandemic. DESIGN: Single-centre retrospective case–control study. SETTING: Tertiary hospital in Germany. PARTICIPANTS: One thousand three hundred and sixteen adult inpatients infected with SARS-CoV-2 and 218 adult inpatients infected with influenza virus. METHODS: Demographic data, outcome parameters and underlying comorbidities of patients were obtained from the hospital information system. Multi-variate regression analysis was performed for the assessment of significant associations between risk factors and outcome variables. RESULTS: Compared with inpatients infected with influenza virus, patients infected with SARS-CoV-2 showed significantly higher rates for in-hospital mortality, admission to ICU and requirement for MV in the wild-type, Alpha and Delta waves, and a significantly higher rate for requirement for ECMO in the wild-type wave. In the Omicron BA.1/BA.2 and Omicron BA.5 waves, patients infected with SARS-CoV-2 did not show significantly higher risk of in-hospital mortality, admission to ICU, or requirement for MV or ECMO compared with patients infected with influenza virus. The length of hospital stay of patients infected with SARS-CoV-2 decreased from 10.8 to 6.2 days, which was less than that of patients infected with influenza virus (8.3 days). CONCLUSIONS: Treatment capacities should be shared equally between SARS-CoV-2 and influenza virus infections. Similar levels of infection control could be applied, at least regarding the severity of infection.