Background: As of October 2020, COVID-19 has caused 1,000,000 deaths worldwide However, large-scale studies of COVID-19 mortality and new-onset comorbidity compared to individuals tested negative for COVID-19 and individuals tested for influenza A/B are lacking We investigated COVID-19 30-day mortality and new-onset comorbidity compared to individuals with negative COVID-19 test results and individuals tested for influenza A/B Methods and findings: This population-based cohort study utilized electronic health records covering roughly half (n = 2,647,229) of Denmark's population, with nationwide linkage of microbiology test results and death records All individuals ≥18 years tested for COVID-19 and individuals tested for influenza A/B were followed from 11/2017 to 06/2020 Main outcome was 30-day mortality after a test for either COVID-19 or influenza Secondary outcomes were major comorbidity diagnoses 30-days after the test for either COVID-19 or influenza A/B In total, 224,639 individuals were tested for COVID-19 To enhance comparability, we stratified the population for in- and outpatient status at the time of testing Among inpatients positive for COVID-19, 356 of 1,657 (21%) died within 30 days, which was a 3 0 to 3 1-fold increased 30-day mortality rate, when compared to influenza and COVID-19-negative inpatients (all p &lt; 0 001) For outpatients, 128 of 6,263 (2%) COVID-19-positive patients died within 30 days, which was a 5 5 to 6 9-fold increased mortality rate compared to individuals tested negative for COVID-19 or individuals tested positive or negative for influenza, respectively (all p &lt; 0 001) Compared to hospitalized patients with influenza A/B, new-onset ischemic stroke, diabetes and nephropathy occurred more frequently in inpatients with COVID-19 (all p &lt; 0 05) Conclusions: In this population-based study comparing COVID-19 positive with COVID-19 negative individuals and individuals tested for influenza, COVID-19 was associated with increased rates of major systemic and vascular comorbidity and substantially higher mortality Results should be interpreted with caution because of differences in test strategies for COVID-19 and influenza, use of aggregated data, the limited 30-day follow-up and the possibility for changing mortality rates as the pandemic unfolds However, the true COVID-19 mortality may even be higher than the stated 3 0 to 5 5-fold increase, owing to more extensive testing for COVID-19
Thirty-Day Mortality and Morbidity in COVID-19 Positive vs. COVID-19 Negative Individuals and vs. Individuals Tested for Influenza A/B: A Population-Based Study