Impact of comorbidities on the risk of death and hospitalization among confirmed cases of COVID-19 during the first months of the pandemic in Québec

During the first months of the pandemic, the SARS-CoV-2 virus infected more than 50,000 people in Québec, with more than 6,000 of them requiring hospitalization and more than 5,000 of the cases resulting in death. The identification of risk factors associated with increased severity of COVID-19 was quickly identified as a research priority in countries affected by the pandemic. The presence of pre-existing medical conditions in COVID-19 cases was soon identified as a risk factor for complications that could lead to death (Guan et al., 2020; Reilev et al., 2020; Williamson et al., 2020). Quickly, the COVID-19 surveillance and monitoring team at the Institut national de santé publique du Québec was able to document pre-existing medical conditions for all cases of COVID-19 confirmed by a laboratory or epidemiological link in Québec.

Several studies conducted primarily in Asia identified that several chronic diseases including hypertension, respiratory disorders, cardiovascular diseases and autoimmune diseases appear to be associated with an increasing risk of death or hospitalization in people with COVID-19 (Guan, 2020; Liang, 2020; Reilev, 2020; Sun, 2020; Williamson, 2020; Zeng, 2020). Currently, no studies assessing the impact of pre-existing conditions have been conducted in Québec.

Identification of comorbidities associated with death or hospitalization in cases of COVID-19 in Québec will make it possible to identify subgroups of the population where the application of infection prevention or control measures (including vaccination) would be more beneficial in limiting the burden and complications associated with COVID-19.


This report aims to quantify the effect of comorbidities on the risk of death in confirmed COVID-19 cases. Specifically, its objectives are: 1) to identify comorbidities associated with the risk of death; 2) to evaluate the impact of the number of comorbidities on the risk of death according to living environment and age. In a secondary analysis, we looked at the impact of comorbidities on the risk of hospitalization.


  • Of the confirmed cases of COVID-19 from February to July 2020, nearly 55% of those affected had at least one pre-existing medical condition, compared to 40% in the general population.
    • Among deceased cases, there was a pre-existing medical condition in 97% of cases. Of those who were hospitalized, 87% had a pre-existing medical condition.
  • Fourteen comorbidities were identified as having an impact on the risk of death and 17 on the risk of hospitalization. The most prevalent comorbidities include: cardiovascular diseases, respiratory diseases, diabetes and anaemia.
  • The number of comorbidities has an impact on the risk of death and hospitalization in confirmed cases of COVID-19.
  • The impact of the number of comorbidities varies according to age and living environment.
    • In a confirmed case of COVID-19 under 60 years of age living at home and with only one comorbidity, the risk of death is five times higher than for someone of the same age with no comorbidities. Excess risk decreases with age.
    • The number of comorbidities has a small impact on death among individuals aged 80 and over residing in long-term care facilities, known in Québec as “centre d’hébergement et de soins de longue durée” (CHSLDs), or private seniors’ residences, known in Québec as “résidence privée pour aînés” (RPAs).
Louis Rochette
Institut national de santé publique du Québec
Marjolaine Dubé
B. Sc., conseillère scientifique, Direction de la santé environnementale et de la toxicologie
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