In patients with uncomplicated influenza, bronchoscopy typically reveals diffuse inflammation and edema of the larynx, trachea, and bronchi, and biopsy may show cellular infiltration with lymphocytes and histocytes and desquamation of the ciliated columnar epithelium [25] . In patients with severe influenza infections that progress to primary viral pneumonia, the involvement of the respiratory tree is extensive, with necrotizing tracheobronchitis, ulceration and sloughing of the bronchial mucosa [26] , hyperemic alveolar capillaries with intra-alveolar hemorrhage, infiltration of alveolar spaces with fluid, fibrin, and cellular exudates, and lining of the alveoli with acellular hyaline membranes [1] . Autopsies from patients with primary influenza pneumonia confirmed bilateral severe hemorrhagic pneumonitis with interstitial inflammation, diffuse alveolar damage, and heavy viral loads observed in the periphery of the lungs.