HPIV-1, HPIV-2 and HPIV-3 cause lower respiratory infections. Upper respiratory infections (URI) are also important in the context of HPIV, however, they are caused to a lesser extent by the virus.
The highest rates of serious HPIV illnesses occur among young children, and surveys have shown that about 75% of children aged 5 or older have antibodies to HPIV-1.
Repeated infection throughout the life of the host is not uncommon and symptoms of later breakouts include upper respiratory tract illness, such as cold and a sore throat.
HPIV-1 and HPIV-2 have been demonstrated to be the principal causative agent behind croup (laryngotracheobronchitis), which is a viral disease of the upper airway and is mainly problematic in children aged 6–48 months of age.
Important epidemiological factors that are associated with a higher risk of infection and mortality are those who are immuno-compromised and may be taken ill with more extreme forms of LRI. Associations between HPIVs and neurologic disease are known; for example, hospitalisation with certain HPIVs has a strong association with febrile seizures. HPIV-4B has the strongest association (up to 62%) followed by hPIV-3 and -1.
HPIVs have also been linked with rare cases of virally caused meningitis and Guillain–Barré syndrome.