Covid-19 has led to a health crisis, with millions of deaths globally. Recently, reports of cardiovascular complications have been increasing. Previous studies on the risk of venous thromboembolism after covid-19 have shown conflicting results. Large nationwide studies are needed to better determine the risks of venous thromboembolism after covid-19.
In order to quantify the risk of deep vein thrombosis, pulmonary embolism, and bleeding after covid-19, 1?057?174 people who tested positive for SARS-CoV-2 between 1 February 2020 and 25 May 2021 in Sweden, matched on age, sex, and county of residence to 4?076?342 control participants. Self-controlled case series and conditional Poisson regression were used to determine the incidence rate ratio and risk ratio with corresponding 95% confidence intervals for a first deep vein thrombosis, pulmonary embolism, or bleeding event. In the self-controlled case series, the incidence rate ratios for first time outcomes after covid-19 were determined using set time intervals and the spline model. The risk ratios for first time and all events were determined during days 1-30 after covid-19 or index date using the matched cohort study, and adjusting for potential confounders (comorbidities, cancer, surgery, long term anticoagulation treatment, previous venous thromboembolism, or previous bleeding event).
During the self-controlled case series period, 1761 participants had a first deep vein thrombosis event; of these 783 (44.5%) were female participants and 978 (55.5%) male participants. Compared with the control period, the incidence rate ratios of a first deep vein thrombosis were 5.59 (95% confidence interval 4.47 to 6.98) during the first week after covid-19 and 7.44 (6.06 to 9.14) during the second week and significantly increased up to 70 days and also during the period before exposure to SARS-CoV-2 (?3 days to day 0) and in the 30 days before covid-19. During the self-controlled case series period, 3267 participants had a first pulmonary embolism. The incidence rate ratio of a first pulmonary embolism was 36.17 (31.55 to 41.47) during the first week after covid-19 and 46.40 (40.61 to 53.02) during the second week compared with the control period and significantly increased up to 110 days and also during the period before exposure to SARS-CoV-2 (?3 days to day 0) and the 30 days before covid-19. During the self-controlled case series period, 7927 participants had a first bleeding event. The incidence rate ratio of a first bleeding event was 3.46 (3.09 to 3.87) during the first week after covid-19 and 2.75 (2.42 to 3.13) during the second week compared with the control period, and significantly increased up to 60 days and also during the period before exposure to SARS-CoV-2 (?3 days to day 0) and the month before covid-19.
The findings of this study suggest that covid-19 is a risk factor for deep vein thrombosis, pulmonary embolism, and bleeding. These results could impact recommendations on diagnostic and prophylactic strategies against venous thromboembolism after covid-19.