Assessing the impact of COVID-19 on mortality: A population-based matched case-control study

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Clinical Microbiology and Infection

Abstract

Objective

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

Methods

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

Results

A total of 2874 patients who died were successfully matched to 2874 living controls. The prevalence of COVID-19 was higher among patients who died compared to controls [13.5% (387/2874) vs. 4% (115/2874), respectively; odds ratio(OR) 3.73; 95% confidence interval(CI) 3.01–4.63, P<0.001). A significantly increased odds of mortality was also observed in COVID-19 patients without underlying diseases (OR, 3.67; 95% CI 2.58-5.23), and in COVID-19 patients with underlying diseases (OR, 3.77; 95% CI 2.87-4.94). Multivariable logistic analysis showed that COVID-19 (OR 2.01; 95% CI 1.07-3.77), low socioeconomic 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 while influenza vaccination and high body mass index were associated with lower rates of mortality.

Conclusion

Testing positive for COVID-19 increased the risk of death threefold, 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 vaccine or effective therapeutics were available.

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