Risk of thrombotic complications in influenza versus COVID-19 hospitalized patients

Stals, M. A.; Grootenboers, M. J.; van Guldener, C.; Kaptein, F. H.; Braken, S. J.; Chen, Q.; Chu, G.; van Driel, E. M.; Iglesias del Sol, A.; de Jonge, E.; Kant, K. M.; Pals, F.; Toorop, M. M.; Cannegieter, S. C.; Klok, F. A.; Huisman, M. V.; Coalition, Dutch COVID and Thrombosis

Background: Whereas accumulating studies on COVID19 patients report high incidences of thrombotic complications, large studies on clinically relevant thrombosis in patients with other respiratory tract infections are lacking. How this high risk in COVID19 patients compares to those observed in hospitalized patients with other viral pneumonias such as influenza is unknown. Objectives: To assess the incidence of venous and arterial thrombotic complications in hospitalized influenza patients as opposed to that observed in hospitalized COVID19 patients. Methods: Retrospective cohort study; we used data from Statistics Netherlands (study period: 2018) on thrombotic complications in hospitalized influenza patients. In parallel, we assessed the cumulative incidence of thrombotic complications, adjusted for competing risk of death, in patients with COVID19 in three Dutch hospitals (February 24th - April 26th 2020). Results: Of the 13.217 hospitalized influenza patients, 437 (3.3%) were diagnosed with thrombotic complications, versus 66 (11%) of the 579 hospitalized COVID19 patients. The 30 day cumulative incidence of any thrombotic complication in influenza was 11% (95%CI 9.4-12) versus 25% (95%CI 18-32) in COVID19. For venous thrombotic complications (VTE) and arterial thrombotic complications alone, these numbers were respectively 3.6% (95%CI 2.7-4.6) and 7.5% (95%CI 6.3-8.8) in influenza versus 23% (95%CI 16-29) and 4.4% (95%CI 1.9-8.8) in COVID19. Conclusions: The incidence of thrombotic complications in hospitalized influenza patients was lower than in hospitalized COVID19 patients in our study. This difference was mainly driven by a high risk of VTE complications in the COVID19 patients admitted to ICU. Remarkably, influenza patients were more often diagnosed with arterial thrombotic complications.