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Thrombotic Events Not Uncommon in Non–COVID-19 Viral Pneumonia

Key findings

  • Studies suggest high rates of thrombotic events in patients hospitalized with COVID-19, but whether thrombosis is typical of viral pneumonia was unknown
  • In this nationwide observational study of 455,629 hospitalizations for viral pneumonia, acute thrombotic events were not uncommon (incidence of 3.0%)
  • Baseline characteristics and comorbidities associated with increased likelihood of thrombotic events included carotid artery disease, age greater than or equal to 75, heart failure, cancer, coronary artery disease, peripheral vascular disease and valvular heart disease
  • Development of thrombotic events was associated with increased in-hospital mortality, longer hospital stay, higher hospital costs and increased likelihood of discharge to skilled nursing care

Anecdotal and published reports suggest rates of thrombotic events are high in patients hospitalized with COVID-19. These observations lack context, though, because little research has described thrombotic events among patients with viral pneumonia unrelated to COVID-19.

Islam Elgendy, MD, interventional cardiologist and vascular interventional fellow, Dhaval Kolte, MBBS, PhD, MBBS, interventional cardiologist, both of the Corrigan Minehan Heart Center at Massachusetts General Hospital; Mazen S. Albaghdadi, MD, MSc, interventional cardiologist currently clinically based at Toronto General Hospital; and colleagues addressed this knowledge gap by reviewing a nationally representative dataset. In a letter to the editor of The American Journal of Cardiology, they say thrombotic events in patients with viral pneumonia were not uncommon prior to COVID-19 (incidence of 3.0%).

Study Methods

The researchers analyzed the National Inpatient Sample for data on 455,629 hospitalizations with a primary diagnosis of viral pneumonia, including those unrelated to influenza (14%). The study covered the years 2005–2015.


13,465 patients (3%) had thrombotic events:

  • Acute myocardial infarction: 1.3%
  • Venous thromboembolism: 1.0%
  • Acute ischemic stroke: 0.7%
  • Acute limb ischemia: 0.05%


On multivariable analysis, mechanical ventilation was associated with the highest risk of thrombotic events (OR, 3.96).

Some of the other independently associated variables were carotid artery disease, acute respiratory failure, other insurance (vs. private), age ≥75, sepsis, heart failure, cancer, known coronary artery disease, septic shock, weight loss, peripheral vascular disease and valvular heart disease.


Compared with patients who did not have thrombotic events, those who did:

  • Had higher in-hospital mortality (12.8% vs. 1.8%; adjusted OR, 1.68; P<0.001)
  • Had longer hospital stays (10.1 vs. 4.5 days; adjusted parameter estimate, 2.94 days, P<0.001)
  • Had higher hospital costs ($30,782 vs. $9,641; adjusted parameter estimate, $9,322; P<0.001)
  • Were more likely to be discharged to a skilled nursing facility (41% vs. 17%; adjusted OR, 2.11; P<0.001)
  • These findings may serve as a comparator once similar data are available for pneumonia related to COVID-19

incidence of thrombotic events among hospitalized patients with viral pneumonia unrelated to COVID-19

greater odds of thrombotic events in hospitalized patients with viral pneumonia unrelated to COVID-19 who required mechanical ventilation versus those who did not

greater odds of in-hospital death in patients with viral pneumonia unrelated to COVID-19 who had thrombotic events than in those without thrombosis

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