Incidence of Venous and Arterial Thromboembolism in Hospitalized and Non-Hospitalized COVID-19 Patients

Available literature on thrombosis occurrence in COVID-19 patients focuses on hospitalized cases. A new study sheds light on the incidence of thromboembolism in less severe cases of disease,

Thromboembolism is a known complication of COVID-19 infection, although to date almost all data has focused on hospitalized COVID-19 patients. A team of scientists conducted a study examining the number of thrombosis cases in people diagnosed with COVID-19 but not hospitalized, then compared the findings to the data on people hospitalized with COVID-19. The study was published in The Lancet.

The research team accessed health records from the Netherlands, Italy, Spain, the United Kingdom, and Germany, including 909,473 individuals with COVID-19 who were not hospitalized and 32,329 patients in Spain who were hospitalized with COVID-19. They followed the subjects’ health journeys for a period of 90 days from COVID-19 diagnosis, noting the incidence of venous and arterial thromboembolism during that time. The mortality rate among each cohort during that time also was calculated.

Over a 90-day period beginning with COVID-19 diagnosis or a positive PCR test, subjects who were not hospitalized experienced venous thromboembolism at rates ranging from 0.21% (95% confidence interval, 0.16-0.27) in the Netherlands to 0.80% (95% CI, 0.77-0.83) in Spain. Covid-19 patients in Italy experienced venous thromboembolism at a rate of 0.27% (95% CI, 0.21-0.25), UK patients had a rate of 0.27% (95% CI, 0.26-0.29), and German COVID-19 patients’ rate was 0.44% (95% CI, 0.36-0.53). For hospitalized patients in Spain, the 90-day incidence of venous thromboembolism was 4.52% (95% CI, 4.37-4.68).

Rates of arterial embolism in non-hospitalized patients ranged from 0.06% (95% CI, 0.05-0.07) in the UK and Italy (95% CI, 0.04-.11) to 0.79% (95% CI, 0.77-0.82) in Spain. In non-hospitalized patients in the Netherlands the arterial embolism rate was 0.10% (95% CI, 0.07-0.15), while in Germany it was 0.18% (95% CI, 0.12-0.23). The rate rose to 3.08% (95% CI, 2.96-3.21) in hospitalized Covid-19 patients in Spain.

The authors noted that the higher rates of embolism seen in the cohort of patients in Spain, even in non-hospitalized individuals, is likely due to the fact that the data coming from Spain was particularly comprehensive (covering 80% of the population of the region of Catalonia) and linked to hospital databases. This “probably indicat[es] underreporting in datasets based solely on primary care records,” they wrote.

The death rate for COVID-19-positive but not hospitalized individuals in the 90-day period after diagnosis or positive PCR test ranged from 1.08% (95% CR, 0.96-1.20) in the Netherlands to 1.99% (95% CI, 1.95-2.03) in Spain, while the death rate for hospitalized Covid-19 patients was 14.61% (95% CI, 14.22-15.00). Venous and arterial thromboembolism that occurred after Covid-19 infection but before hospitalization was associated with higher rates of hospitalization and death. Venous and arterial thromboembolisms occurring after hospitalization also corresponded with higher mortality rates.

The study found that being male was associated with a higher risk of arterial thromboembolism and death; venous thromboembolism risk was higher in men in all locations except for Germany and Italy. The authors reported that venous and arterial thromboembolism and death rates among non-hospitalized Covid-19 patients generally were higher for people 65 years old and above. In the hospitalized cohort, the 65-plus age group had a higher risk of arterial thromboembolism and death, but not venous thromboembolism, which seemed to peak at about age 70 and then level off or decline. “This is probably largely explained by the substantial competing risk of death for those with COVID-19, which is much increased with older age,” they wrote.