A case report series of influenza A virus-induced pulmonary disease with diverse clinical manifestations.

Background: Influenza A virus (IAV) typically causes influenza-like symptoms; however, in patients with underlying chronic respiratory diseases, it may progress to severe pneumonia and acute respiratory distress syndrome (ARDS). In addition to parenchymal lung injury, some patients may develop severe airway hyperresponsiveness (AHR), including bronchospasm, mucus plug formation, and refractory carbon dioxide retention, often resulting in poor responses to conventional respiratory support. Methods: This study reports three cases of IAV-associated pulmonary disease complicated by respiratory failure. Two patients were elderly men with COPD who presented with refractory AHR and carbon dioxide retention, despite the absence of severe pulmonary infection on imaging. The third patient was a middle-aged man without underlying disease whose chest imaging demonstrated severe pneumonia. All three patients received comprehensive treatment centered on respiratory support, including high-flow oxygen therapy, invasive mechanical ventilation, and individualized antimicrobial therapy; one patient additionally received veno-venous extracorporeal membrane oxygenation (VV-ECMO) support. Results: Despite aggressive treatment, including VV-ECMO support in one patient, the two patients with COPD experienced unfavorable outcomes. Case 1 developed persistent refractory AHR and progressive ventilatory failure, while Case 3 deteriorated in the context of multiple complications. In contrast, the patient without underlying disease, despite severe pneumonia on chest CT, recovered and was discharged following treatment with high-flow nasal oxygen therapy alone. Conclusion: In this case series, the clinical outcomes of IAV-associated pulmonary disease appeared to differ according to underlying pulmonary conditions. Patients with COPD exhibited more persistent AHR and ventilatory failure, whereas the patient without chronic respiratory disease showed reversible airway dysfunction and favorable recovery. These observations suggest that underlying respiratory status may influence the clinical course of IAV-associated AHR; however, further studies are required to validate these findings.