Venous Thromboembolism and COVID-19—an Epidemiological Perspective

The coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was declared as pandemic by World Health Organization (WHO) in March 2020. The outbreak has caused 5,232,562 deaths worldwide until December 3rd, 2021. Though primarily affecting the respiratory system, involvement of other organ systems have been reported in severe disease. Venous thromboembolism (VTE) has been recognized as an important complication. Previous studies have reported the prevalence of VTE in intensive care unit (ICU) patients between 7 and 85% and in non-ICU patients between 0 and 19%. COVID-19 patients that are at high risk for VTE are also at increased risk for bleeding. In such cases, anticoagulation may potentially be harmful. Thereby, it is important to understand the risk factors for VTE predisposition in the COVID-19 patients, timing of VTE, and the rate of occurrence of VTE in hospitalized patients post-discharge. Comparison of the rate of occurrence of VTE in COVID-19 patients with the non-COVID-19 patients with similar disease severity is required to truly interpret the reportedly high rates of VTE in COVID-19 patients. Several pathophysiological mechanisms have been reported for the development of VTE in COVID-19. Autopsy-based studies have contributed to the existing knowledge. d-dimer, presently, seems to be the most suitable investigation for risk-identification of VTE supported by Doppler studies and overall clinical context. Further, prospective studies and clinical trials are essentially required to fill the gaps in evidence for occurrence, risk prediction and management of VTE in COVID-19 patients.