Change in patterns of hospitalization for influenza during COVID-19 surges

Abstract

Background: Hospitalization due to influenza has been stable in recent years. In March 2020, New York was an epicenter for coronavirus disease 2019 (COVID-19). Because influenza and COVID-19 present similarly, there were serious concerns that coinfection of these viruses would burden the healthcare system. We compared incidence and outcomes of patients hospitalized with influenza before and during COVID-19 (seasons 2017-2021).

Methods: We conducted a retrospective study evaluating hospitalized patients with influenza. Four influenza seasons were evaluated, 2017-2021, pre- and during COVID-19 pandemic. We compared incidence of influenza and clinical outcomes across the seasons.

Results: We found 412 patients hospitalized due to influenza in the study period; 394 had influenza, and 18 had both influenza and COVID-19 infections. Demographics across the four influenza seasons were comparable; the cohort was predominantly female (61%) and had an average age of 60 years old. Comorbid conditions were common. No outcome differences were found for patients with influenza when comparing influenza seasons prior to and during the COVID-19 pandemic. The mortality for the entire cohort was 6.5%. During the COVID-19 pandemic, there were 18 (4.4%) influenza patients coinfected with COVID-19 and 32 (7.8%) patients with bacterial super infection. Predictors of mortality in patients with influenza included presence of shock, heart failure, bacterial pneumonia, and use of mechanical ventilation. Coinfection with COVID-19 did not increase mortality.

Conclusion: We observed a significant decrease in the incidence of hospitalization due to influenza during the COVID-19 pandemic. Clinical presentations and outcomes for patients with influenza remain stable. Being aware of possible increased mortality for patients with both influenza and bacterial pneumonia is important. Although coinfection with COVID-19 did not increase mortality in influenza patients, identifying the specific virus responsible for infections has major therapeutic implications.

Keywords: COVID-19; influenza; mechanical ventilation; mortality; pneumonia.