Comparison of Critical Care Occupancy and Outcomes of Critically ill Patients during the 2020 COVID-19 Winter Surge and 2009 H1N1 Influenza Pandemic in Australia.

RATIONALE: Both 2009 pandemic influenza A (H1N1) and SARS-CoV-2 are transmitted by respiratory secretions and in severe cases result in a viral pneumonitis, requiring intensive care unit (ICU) admission. However, no studies have compared the clinical characteristics and outcomes of such patients. OBJECTIVES: To report and compare the demographic characteristics, treatments, use of critical care resources, and outcomes of patients admitted to an Australian ICU with H1N1 influenza during the winter of 2009, and SARS-CoV-2, during the winter of 2020. METHODS: This was a multicentre project, utilizing national data from previous and ongoing epidemiological studies concerning severe acute respiratory infections in Australia. All ICUs admitting patients with H1N1 or COVID-19 were included and contributed data. We compared clinical characteristics and outcomes of H1N1 patients admitted to ICU in the winter of 2009 vs COVID-19 patients admitted to ICU in the winter of 2020. The primary outcome was in-hospital mortality. Potential years of life lost (PYLL) was calculated according to sex-adjusted life expectancy in Australia. RESULTS: Across the two epochs, 861 patients were admitted to ICUs; 236 (27.4%) with COVID-19, and 625 (72.6%) with H1N1 influenza. The number of ICU admissions and bed-days occupied were higher with 2009 H1N1 influenza. COVID-19 patients were older, more often male and overweight, and had lower APACHE 2 at ICU admission. The highest age-specific incidence of ICU admission was among infants (0 to 1 year of age) for H1N1, and among the elderly (≥ 65 years) for COVID-19. Unadjusted in-hospital mortality was similar (11.5% in COVID-19 vs. 16.1% in H1N1; odds ratio, 0.68 [95% confidence interval, 0.42 to 1.06]; p = 0.10). The PYLL was greater with H1N1 influenza than with COVID-19 at 154.1 (95% CI, 148.7 to 159.4) vs 13.6 (95% CI, 12.2 to 15.1) PYLL per million inhabitants. CONCLUSIONS: In comparison to 2009 H1N1 influenza, COVID-19 admissions over winter in Australia resulted in fewer ICU admissions, and lower bed-day occupancy. Crude in-hospital mortality was similar, but because of demographic differences in affected patients, deaths due to 2009 H1N1 influenza led to an 11-fold increase in the number of PYLL in critically ill patients.