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-4 remains infrequently detected. However, it is now believed to be more common than previously thought, but is less likely to cause severe disease. By the age of 10, the majority of children are sero-positive for HPIV-4 infection which may be indicative of a large proportion of asymptomatic or mild infections.
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.