A respiratory system infectious disease that involves inflammation, edema, and subsequent obstruction of the larynx, trachea, and bronchi. The disease is caused by viruses, bacteria, allergies and inhaled irritants. It is marked by episodes of difficult breathing and hoarse metallic cough in infants and young children. Croup is caused by parainfluenza virus (types 1 and 2), Influenza A and B viruses, Measles virus, adenovirus, respiratory syncytial virus, Staphylococcus and Streptococcus.