Human parainfluenza viruses (HPIVs) are a group of organisms, types 1 through 4, that cause several different respiratory infections. For example, they are the major cause of croup, which is an inflammation of the voice box (larynx) and windpipe (trachea) that makes breathing more difficult. They also cause some cases of lower respiratory tract diseases, including pneumonia (a lung infection) and bronchiolitis (an infection of the lung’s small breathing tubes). They can make the symptoms of chronic lung disease worse in children.
Parainfluenza viruses have an incubation period of 2 to 6 days. They are spread from person to person by direct contact or exposure to contaminated secretions from the nose or throat. Children are usually exposed to most types of parainfluenza by 5 years of age.