Assessing the impact of coronavirus disease 2019 on mortality: a population-based, matched case-control study

Estimating the isolated effect of coronavirus disease 2019 (COVID-19) on the risk of mortality is challenging. We aimed to determine whether COVID-19 was associated with high rates of mortality independently of age, sex and underlying disorders.

A population-based, matched, case-control study of adults insured by Clalit Health Services was performed. Cases were defined as patients who died of all causes between July and December 2020. Each case was matched in a ratio of 1:1 with a living control based on age, sex and co-morbidities. An unconditional logistic regression analysis was performed to identify independent risk factors for mortality.

A total of 2874 patients who died were successfully matched with 2874 living controls. The prevalence of COVID-19 was higher among the patients who died than among the controls (13.5% [387/2874] vs. 4% [115/2874], respectively; OR, 3.73; 95% CI, 3.01-4.63; p < 0.001). A significantly increased odds of mortality was also observed in patients with COVID-19 without underlying diseases (OR, 3.67; 95% CI, 2.58-5.23) and in patients with COVID-19 and underlying diseases (OR, 3.77; 95% CI, 2.87-4.94). A multi-variate logistic analysis showed that COVID-19 (OR, 2.01; 95% CI, 1.07-3.77), low socio-economic status (OR, 1.36; 95% CI, 1.02-1.82), dementia (OR, 2.50; 95% CI, 2.10-3.01), smoking (OR, 1.35; 95% CI, 1.13-1.63) and an interaction variable of age >80 years and COVID-19 (OR, 2.27; 95% CI, 1.14-4.54) were independent risk factors for mortality, whereas influenza vaccination and high body mass index were associated with lower rates of mortality.

Testing positive for COVID-19 increased the risk of death three folds, regardless of underlying disorders. These results emphasize the effect of COVID-19 on mortality during the early period of the COVID-19 outbreak, when no vaccines or effective therapeutics were available.