Influenza A and Pulmonary Embolism Risk
Yes, influenza A infection can increase the risk of developing pulmonary emboli, particularly in severe cases, though the association is not consistently observed across all studies.
Pathophysiological Relationship Between Influenza and Thromboembolism
Influenza infections, particularly severe cases, can create conditions favorable for thromboembolic events through several mechanisms:
- Inflammatory Response: Severe influenza can trigger a significant inflammatory response that may promote a hypercoagulable state
- Endothelial Damage: Viral infection can damage the vascular endothelium, potentially initiating the coagulation cascade
- Immobilization: Severe illness often leads to reduced mobility, a known risk factor for venous thromboembolism
Evidence for the Association
The evidence regarding the relationship between influenza A and pulmonary embolism is mixed:
Supporting Evidence
A scoping review found that among 58 cases of thromboembolic events associated with laboratory-confirmed influenza, pulmonary embolism was the most common manifestation (36.2% of cases) 1
Case reports have documented acute pulmonary microthromboembolism in patients with influenza A(H3N2) virus infection who presented with rapidly progressive hypoxemia 2
A case series of patients with H1N1 influenza found that 6 out of 7 patients developed pulmonary embolism without deep vein thrombosis while hospitalized for influenza pneumonia 3
Individual case reports have documented concurrent thrombotic events including pulmonary embolism in patients with influenza-associated pneumonia 4
Contradictory Evidence
- A nested case-control study did not find an association between influenza infection and increased risk of acute pulmonary embolism. In fact, the percentage of patients with influenza A was higher in the control group compared to patients with confirmed pulmonary embolism (4.3% versus 1.0%) 5
Clinical Implications
High-Risk Populations
Certain groups may be at higher risk for complications including thromboembolic events:
- Elderly patients
- Patients with underlying cardiopulmonary disease
- Immunocompromised individuals
- Pregnant women
- People with diabetes
Diagnostic Challenges
Symptoms of pulmonary embolism can overlap with those of severe influenza, making diagnosis challenging:
- Both conditions can present with dyspnea, hypoxemia, and respiratory distress
- Careful clinical evaluation is essential, as highlighted in the scoping review 1
Management Considerations
For patients with severe influenza, especially those with risk factors for thromboembolism:
- Consider thromboprophylaxis in hospitalized patients with severe influenza
- Maintain high clinical suspicion for pulmonary embolism in patients with unexplained or disproportionate dyspnea
- Appropriate diagnostic workup may include D-dimer testing, ventilation-perfusion scanning, or CT pulmonary angiography in suspected cases
Conclusion
While not all studies show a consistent association, there is evidence suggesting that influenza A infection, particularly severe cases requiring hospitalization, may increase the risk of pulmonary embolism. Clinicians should maintain vigilance for thromboembolic complications in patients with severe influenza, especially when respiratory symptoms worsen unexpectedly or are disproportionate to the degree of pulmonary involvement seen on imaging.