Human parainfluenza viruses (HPIVs) belong to the Paramyxoviridae family. They are negative-sense, single-stranded, enveloped RNA viruses. There are four types (1 through 4) and two subtypes (4a and 4b) of HPIVs. The clinical and epidemiological features for each HPIV type can sometimes vary. In the United States, infections associated with HPIV-1 are seen more commonly in odd-numbered years and HPIV-2 and HPIV-3 are seen annually. HPIVs commonly infect infants and young children. However, anyone can get HPIV infection.
The incubation period, the time from exposure to HPIV to onset of symptoms, is generally 2 to 7 days.
- HPIV-1 and HPIV-2 are most often associated with croup. HPIV-1 often causes croup in children, whereas HPIV-2 is less frequently detected. Both types can cause upper and lower respiratory tract illnesses. People with upper respiratory tract illness may have cold-like symptoms.
- HPIV-3 is more often associated with bronchiolitis, bronchitis, and pneumonia.
- HPIV-4 is not recognized as often but may cause mild to severe respiratory tract illnesses.
People can get multiple HPIV infections in their lifetime. These reinfections usually cause mild upper respiratory tract illness with cold-like symptoms. However, reinfections can cause serious lower respiratory tract illness, such as pneumonia, bronchitis, and bronchiolitis in some people. Older adults and people with compromised immune systems, in particular, have a higher risk for severe infections.
Most children 5 years of age and older have antibodies against HPIV-3 and approximately 75% have antibodies against HPIV-1 and HPIV-2.
HPIVs usually spread by direct contact with infectious droplets or by airborne spread when an infected person breathes, coughs, or sneezes.
HPIVs may remain infectious in airborne droplets for over an hour and on surfaces for a few hours depending on environmental conditions.
People are most contagious during the early stage of illness.
People usually get HPIV infection in the spring, summer, and fall. However, it is possible to get infected at any time of the year. For more information, see HPIV Seasons.
Currently, there is no vaccine to prevent HPIV infection. However, researchers are trying to develop vaccines. Also, there is no specific antiviral treatment for HPIV illness. Most HPIV illnesses are mild and typically require only treatment of symptoms.
In hospital settings, healthcare providers should follow contact precautions, such as handwashing and wearing protective gowns and gloves. For more information, see CDC’s 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings.
To help protect patients from HPIV infection, also see Prevention & Treatment.