The risk of  venous thromboembolism or bleeding remains increased for up to six months after Covid-19 infection, according to a study of more than one million people from Sweden published by The BMJ.¹ Patients who had had severe Covid were particularly at high risk.

Researchers set out to measure the risk of deep vein thrombosis, pulmonary embolism, and bleeding after Covid-19 using data from SmiNet, a communicable disease surveillance system in Sweden from February 1, 2020 to May 25, 2021. A total of 1,057,174 patients with lab confirmed Covid-19 were included in this study and they were matched demographically and by county of residence to 4,076,342 persons who were negative for Covid as controls. Only patients with first infections were included in the study. Majority (94.5%) of the study participants had mild infection, 4.8% were hospitalized, while 0.7% were in ICU; mortality was 1.8%.

A significant increase in the incidence rate ratios was noted 70 days after Covid-19 for deep vein thrombosis, 110 days for pulmonary embolism and 60 days for bleeding. During the first week, the incidence rate ratios for a first pulmonary embolism were 36.17, which increased to 46.40 during the second week.

The incidence rate ratios in the first 30 days after covid-19 were 5.90 for deep vein thrombosis, 31.59 for pulmonary embolism and 2.48 for bleeding. The risk for DVT increased 5-folds (risk ratio 4.98) during the first 30 days after Covid-19 and the risk for bleeding doubled (RR 1.88) compared to matched controls. However, the risk for a first pulmonary embolism was increased 33 times (RR 33.05). Critically ill patients were at highest risk of DVT, PE or bleeding. The risk ratios were also higher during the first pandemic wave in Sweden compared with the second and third waves.

The risk of DVT and PE was also increased among patients with mild Covid-19, although there was no increase in the risk of bleeding in these patients.

Covid-19 induces a hyperinflammatory and hypercoagulable state in the body. These observations show Covid-19 to be an independent risk factor for deep vein thrombosis, pulmonary embolism and bleeding, especially in patients with severe disease and also shed light on the duration for the increased risk. The risk for DVT was high up to three months post-Covid, up to 6 months for pulmonary embolism and up to two months for bleeding. Hence, even though the pandemic is seemingly receding, these results highlight the need to be constantly vigilant about the risk of thromboembolism in Covid-19 patients, including in those who had mild infections. It further supports thromboprophylaxis in Covid-19 patients, particularly for the high-risk patients to prevent thromboembolic episodes.

Reference

1. Katsoularis I, et al. Risks of deep vein thrombosis, pulmonary embolism, and bleeding after COVID-19: nationwide self-controlled cases series and matched cohort study. BMJ 2022 Apr 6; 377: e069590. doi: https://doi.org/10.1136/bmj-2021-069590.