Incidence and determinants of venous thromboembolism over 90 days in hospitalized and nonhospitalized patients with COVID-19.

Introduction: COVID-19 is associated with an increased risk of venous thromboembolism (VTE), but there is great variation among reported incidence rates. Most previous studies have focused on hospitalized patients with COVID-19, and only a few reports are from population-based registries.

Methods: We studied the 90-day incidence of VTE, associated risk factors and all-cause mortality in hospitalized and nonhospitalized patients with COVID-19 in a nationwide cohort. Data on hospitalizations and outpatient visits were extracted from two national registries with mandatory reporting linked by a unique national identification number carried by all Norwegian residents. We performed Cox proportional hazards regression to determine risk factors for VTE after infection with SARS-CoV-2.

Results: Our study included 30,495 patients with positive SARS-CoV-2 polymerase chain reaction with a mean (SD) age of 41.9 (17.3) years, and 53% were males. Only 2081 (6.8%) were hospitalized. The 90-day incidence of VTE was 0.3% (95% CI: 0.21-0.33) overall and 2.9% (95% CI: 2.3-3.7) in hospitalized patients. Age (hazard ratio [HR] 1.28 per decade, 95% CI: 1.11-1.48, p < 0.05), history of previous VTE (HR 4.69, 95% CI: 2.34-9.40, p < 0.05), and hospitalization for COVID-19 (HR 23.83, 95% CI: 13.48-42.13, p < 0.05) were associated with risk of VTE.

Conclusions: The 90-day incidence of VTE in hospitalized and nonhospitalized patients with COVID-19 was in the lower end compared with previous reports, with considerably higher rates in hospitalized than nonhospitalized patients. Risk factors for VTE were consistent with previously reported studies.