Our findings in this acute human infection model are in keeping with clinical studies that have reported associations between chronic mucus hypersecretion/sputum MUC5AC concentrations with airflow limitation and FEV1 decline (10, 21, 30) and an animal study showing that genetic deletion of Muc5ac reduced mucus occlusion and improved lung function in models of allergic airway inflammation (11). Here, MUC5AC is linked to infection.