COVID-19 infection and subsequent thromboembolism: A self-controlled case series analysis of a population cohort

Ho, F.; Man, K.; Toshner, M.; Celis-Morales, C.; Wong, I.; Sattar, N.; Pell, J.

Importance: An unexpectedly large number of people infected with Covid-19 appear to have experienced ischaemic stroke or thrombotic event. Objective: This study aims to assess the risk associations between Covid-19 infection and thromboembolism. Design: This is a self-controlled case-series study in Scotland. Their incidence rates during the risk interval (5 days before to 56 days after the positive test) and the control interval (the remaining periods) were compared intra-personally. Setting: Population-based. Participants: Individuals with confirmed (positive test) Covid-19 and at least one thromboembolic event between March 2018 and October 2020. Exposure: Covid-19 test positive. Main Outcomes and Measures: Myocardial infarction (MI), ischaemic stroke, deep-vein thrombosis (DVT), and pulmonary embolism (PE) hospital admissions and deaths. Results: Across Scotland, 1,449 individuals tested positive for Covid-19 and experienced a thromboembolic event. The risk of thromboembolism was significantly elevated over the whole risk period but highest in the 7 days following the positive test (IRR 12.01, 95% CI 9.91-14.56), especially among people >=75 years (IRR 22.78, 95% CI 17.58-29.53). Risk of MI, stroke, PE and DVT were all significantly higher in the week following a positive test. The risk of PE and DVT was particularly high and remained significantly elevated even 56 days following the test. Conclusions and relevance: Confirmed Covid-19 infection was associated with early elevated risk of MI, ischaemic stroke, and stronger and long elevations in risk with DVT and PE, reinforcing the need to consider monitoring and early diagnosis. Treatment and prevention trials may need to be considered out of hospital on the basis of risk stratification.