Venous or arterial thrombosis and mortality among COVID-19 cases: a European network cohort study

Background: There are limited data on the incidence of thrombosis among COVID-19 cases, with most research concentrated on hospitalised patients. We estimated the incidence of venous thromboembolism (VTE), arterial thromboembolism (ATE), and death among COVID-19 cases; and to assess the impact of these events on hospitalization and mortality. Methods: A distributed network cohort using primary care records from Netherlands, Italy, Spain and the UK; and outpatient specialist records from Germany. The Spanish database was linked to hospital admissions. Participants were followed from a diagnosis of COVID-19 or positive RT-PCR test on or after 1st September 2020. Outcomes included VTE, ATE, hospitalization, and mortality up to 90-days after index date. We estimated cumulative incidences for the study outcomes. Multi-state models were used to study the association between VTE/ATE occurrence and hospitalization and mortality. Results: Overall, 909,473 COVID-19 cases and 32,329 patients hospitalised with COVID-19 were studied. Cumulative 90-day incidence of VTE ranged from 0.2% to 0.8%, and up to 4.5% for those hospitalised. For ATE, estimates ranged from 0.1% to 0.8%, increasing to 3.1% among those hospitalised. Mortality ranged between 1.1% and 2.0%, rising to 14.6% for hospitalised patients. VTE and ATE were associated with worse outcomes. For example, VTE and ATE whilst outpatient resulted in adjusted HR for death of 4.42 [3.07-6.36] and 3.16 [2.65-3.75] respectively. Conclusions and Relevance: Risks of VTE and ATE were up to one percent among COVID-19 cases, but increase with age, among males, and for those hospitalized. Their occurrence is associated with excess mortality, underling the importance of effective treatment strategies that reduce their frequency.