The infection spreads directly through inhalation from a sneeze, coughing, or contamination of hands touching the mucosa of the eyes, nose and mouth. The infection causes the inflammation of larynx, trachea, bronchi, bronchioles, lung parenchyma. Obstruction caused by swelling and inflammatory exudates develops and become pronounced the subglottic region. Obstruction increases the work of breathing, tiring results hypercapnia