Pneumonia in infants commonly occurs in young children, especially those under two years of age. The onset of the disease is usually rapid, starting with symptoms of upper respiratory tract infections that gradually evolve into more pronounced respiratory symptoms. The cough is frequent, initially a dry, irritating cough, that progressively worsens as the disease advances. In cases of severe pneumonia, the cough may actually lessen. During the recovery phase, the cough gradually diminishes and rattling sounds can be heard in the throat due to mucus. After the mucus is cleared, there may still be occasional bouts of irritating dry cough, which will slowly subside.