Epidemiological comparison of emergency department presentations with seasonal influenza or COVID-19 and an outcome of intensive care admission or death: A population-based records linkage study in New South Wales, Australia

Abstract

Background: COVID-19 and seasonal influenza are endemic causes of morbidity and mortality. This study aimed to compare the epidemiology of severe illness and risk of death among patients following emergency department (ED) presentation with either infection.

Methods: De-identified, population-based, emergency department records in New South Wales, Australia, were probabilistically linked to population-level health outcome databases for the period 1 January 2015 to 28 February 2023. Included were patients allocated an ED diagnosis consistent with an acute respiratory infection. Logistic regression was used to examine the association of infecting virus with risk of a severe outcome (intensive care unit admission or death).

Results: Influenza infection was notified in 2335 and COVID-19 in 5053 patients with a severe outcome. The age distribution was similar for both viruses, except in <15-year-olds, where severe influenza was nearly three times more frequent. Overall, the odds of death among patients with COVID-19 was 1.65 (95% CI 1.43, 1.89) times higher than among those with influenza. This declined to 1.49 (95% CI 1.08, 2.06) times during the COVID-19 Omicron variant period.

Conclusions: The Omicron variant arrived when background population COVID-19 vaccination coverage was >90%. Despite that, death was more frequent for COVID-19 than influenza.

Keywords: Covid-19; Death; Epidemiology; Intensive care admission; SARS-CoV-2; Seasonal influenza; Severe illness.