Risk of death from COVID-19 3.5 times higher than from flu — Canadian study

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A study has found that the risk of death from COVID-19 was 3.5 times higher than from influenza. "We can now say definitively that COVID-19 is much more severe than seasonal influenza," says Dr Amol Verma, St Michael's Hospital, Unity Health Toronto, and the University of Toronto. "Patients admitted to hospital in Ontario with COVID-19 had a 3.5 times greater risk of death, 1.5 times greater use of the ICU, and 1.5 times longer hospital stays than patients admitted with influenza."

These findings are similar to study results recently reported in France and the US.

The study compared hospitalisations for influenza between 1 November, 2019, and 30 June, 2020, in 7 large hospitals in Toronto and Mississauga – areas with large populations and high levels of COVID-19. It included all patients admitted to medical services or the intensive care unit (ICU) for influenza or COVID-19. There were 783 hospitalisations for influenza in 763 unique patients compared with 1027 hospitalisations for COVID-19 in 972 unique patients (representing 23.5% of all hospitalisations for COVID-19 in Ontario during the study period).

Most patients hospitalised with COVID-19 had few other illnesses, and 21% were younger than 50 years of age. People younger than 50 also accounted for almost 1 in 4 (24%) admissions to the ICU.

"Many people believe that COVID-19 mainly affects older people," says Verma. "It is true that COVID-19 affects older adults most severely. We found that among adults over 75 years who were hospitalised with COVID-19, nearly 40% died in hospital. But it can also cause very serious illness in younger adults. Adults under 50 accounted for 20% of all COVID-19 hospitalisations in the first wave of the pandemic. Nearly 1 in 3 adults younger than 50 hospitalised with COVID-19 required intensive care, and nearly 1 in 10 required an unplanned readmission to hospital after discharge."

People hospitalised for COVID-19 had greater use of the ICU, were more likely to be put on a ventilator and had longer hospital stays than people with influenza.

"These differences may be magnified by low levels of immunity to the novel coronavirus compared with seasonal influenza, which results from past infections and vaccination," says Verma. "Hopefully, the severity of COVID-19 will decrease over time as people are vaccinated against the virus and more effective treatments are identified. There is, unfortunately, also the possibility that variants of the virus could be even more severe."


Study details
Characteristics and outcomes of hospital admissions for COVID-19 and influenza in the Toronto area

Amol A Verma, Tejasvi Hora, Hae Young Jung, Michael Fralick, Sarah L Malecki, Lauren Lapointe-Shaw, Adina Weinerman, Terence Tang, Janice L Kwan, Jessica J Liu, Shail Rawal, Timothy CY Chan, Angela M Cheung, Laura C Rosella, Marzyeh Ghassemi, Margaret Herridge, Muhammad Mamdani and Fahad Razak

Published in the CMAJ on 10 February 2021

Patient characteristics, clinical care, resource use and outcomes associated with admission to hospital for coronavirus disease 2019 (COVID-19) in Canada are not well described.
We described all adults with COVID-19 or influenza discharged from inpatient medical services and medical–surgical intensive care units (ICUs) between Nov. 1, 2019, and June 30, 2020, at 7 hospitals in Toronto and Mississauga, Ontario. We compared patient outcomes using multivariable regression models, controlling for patient sociodemographic factors and comorbidity level. We validated the accuracy of 7 externally developed risk scores to predict mortality among patients with COVID-19.
There were 1027 hospital admissions with COVID-19 (median age 65 yr, 59.1% male) and 783 with influenza (median age 68 yr, 50.8% male). Patients younger than 50 years accounted for 21.2% of all admissions for COVID-19 and 24.0% of ICU admissions. Compared with influenza, patients with COVID-19 had significantly greater in-hospital mortality (unadjusted 19.9% v. 6.1%, adjusted relative risk [RR] 3.46, 95% confidence interval [CI] 2.56–4.68), ICU use (unadjusted 26.4% v. 18.0%, adjusted RR 1.50, 95% CI 1.25–1.80) and hospital length of stay (unadjusted median 8.7 d v. 4.8 d, adjusted rate ratio 1.45, 95% CI 1.25–1.69). Thirty-day readmission was not significantly different (unadjusted 9.3% v. 9.6%, adjusted RR 0.98, 95% CI 0.70–1.39). Three points-based risk scores for predicting in-hospital mortality showed good discrimination (area under the receiver operating characteristic curve [AUC] ranging from 0.72 to 0.81) and calibration.
During the first wave of the pandemic, admission to hospital for COVID-19 was associated with significantly greater mortality, ICU use and hospital length of stay than influenza. Simple risk scores can predict in-hospital mortality in patients with COVID-19 with good accuracy.


CMAJ study (Open access)



See also MedicalBrief archives:

Public Health England warns that flu doubles risk of COVID-19 death


COVID-19 far deadlier than the flu — University of Washington analysis of 116 counties

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