A retrospective comparison of COVID-19 and seasonal influenza mortality and outcomes in the ICUs of a French university hospital.

Background: SARS-Cov-2 (COVID-19) has become a major worldwide health concern since its appearance in China at the end of 2019.
Objective: To evaluate the intrinsic mortality and burden of COVID-19 and seasonal influenza pneumonia in ICUs in the city of Lyon, France.
Design: A retrospective study.
Setting: Six ICUs in a single institution in Lyon, France.
Patients: Consecutive patients admitted to an ICU with SARS-CoV-2 pneumonia from 27 February to 4 April 2020 (COVID-19 group) and seasonal influenza pneumonia from 1 November 2015 to 30 April 2019 (influenza group). A total of 350 patients were included in the COVID-19 group (18 refused to consent) and 325 in the influenza group (one refused to consent). Diagnosis was confirmed by RT-PCR. Follow-up was completed on 1 April 2021.
Main Outcomes and Measures: Differences in 90-day adjusted-mortality between the COVID-19 and influenza groups were evaluated using a multivariable Cox proportional hazards model.
Results: COVID-19 patients were younger, mostly men and had a higher median BMI, and comorbidities, including immunosuppressive condition or respiratory history were less frequent. In univariate analysis, no significant differences were observed between the two groups regarding in-ICU mortality, 30, 60 and 90-day mortality. After Cox modelling adjusted on age, sex, BMI, cancer, sepsis-related organ failure assessment (SOFA) score, simplified acute physiology score SAPS II score, chronic obstructive pulmonary disease and myocardial infarction, the probability of death associated with COVID-19 was significantly higher in comparison to seasonal influenza [hazard ratio 1.57, 95% CI (1.14 to 2.17); P = 0.006]. The clinical course and morbidity profile of both groups was markedly different; COVID-19 patients had less severe illness at admission (SAPS II score, 37 [28 to 48] vs. 48 [39 to 61], P < 0.001 and SOFA score, 4 [2 to 8] vs. 8 [5 to 11], P < 0.001), but the disease was more severe considering ICU length of stay, duration of mechanical ventilation, PEEP level and prone positioning requirement.
Conclusion: After ICU admission, COVID-19 was associated with an increased risk of death compared with seasonal influenza. Patient characteristics, clinical course and morbidity profile of these diseases is markedly different.
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