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

Abstract

The virulence of SARS-CoV-2 changed during the pandemic. To provide a rationale for treatment priorities of respiratory infections and the adaption of in-house infection control strategies, we evaluated the outcome parameters treatment on an intensive care unit (ICU), requirement of mechanical ventilation (MV), requirement of extracorporeal membrane oxygenation (ECMO) and death for inpatients either 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. Single-centre retrospective case-control study. Tertiary hospital in Germany. 1316 SARS-CoV-2-infected adult inpatients and 218 adult inpatients with seasonal influenza infection. Demographic data, outcome parameters and underlying comorbidities of patients were obtained from the hospital information system. Multivariate regression analysis was performed for the assessment of significant associations between risk factors and outcome variables. Compared to influenza-infected inpatients, SARS-CoV-2-infected inpatients showed significantly evaluated rates for in-hospital mortality, admission to ICU and MV in the wild type, alpha and delta wave and for ECMO in the wild type wave. In the Omicron BA.1/BA.2 and Omicron BA.5 waves, SARS-CoV-2-infected inpatients did not show significantly increased risk of in-hospital mortality, admission to ICU, MV or ECMO compared to influenza- infected inpatients. Length of hospital stay of SARS-CoV-2-infected inpatients decreased from 10.8 to 6.2 days which is below that of influenza-infected inpatients (8.3 days). Treatment capacities should be shared equally between SARS-CoV-2 and influenza virus infections and at least regarding the severity of infections similar levels of infection control could be applied.