The parainfluenza viruses are paramyxoviruses and classified as types 1, 2, 3, and 4. They share antigenic cross-reactivity but tend to cause diseases of different severity. Type 4 has antigenic cross-reactivity with the mumps virus and is an uncommon cause of respiratory disease that requires medical attention.
Childhood outbreaks of parainfluenza virus infections can occur in nurseries, pediatric wards, and schools. Types 1 and 2 tend to cause epidemics in the autumn, with each serotype occurring in alternate years. Type 3 disease is endemic and infects most children < 1 year; incidence is increased in the spring.
Parainfluenza viruses can cause repeated infections, but reinfection generally causes milder illness. Thus, in immunocompetent adults, most infections are asymptomatic or mild.
The most common illness in children is an upper respiratory illness with no or low-grade fever.
Parainfluenza type 1 is a frequent cause of croup (laryngotracheobronchitis), primarily in infants aged 6 to 36 months. Croup begins with common cold symptoms. Later, fever, a barking cough, hoarseness, and stridor develop. Respiratory failure due to upper airway obstruction is a rare but potentially fatal complication. Parainfluenza type 2 can cause similar disease but is typically less severe.
Parainfluenza virus type 3 may cause pneumonia and bronchiolitis in young infants and in immunocompromised children and adults. These illnesses are generally indistinguishable from disease caused by respiratory syncytial virus) but are often less severe.
Usually, a specific viral diagnosis is clinically unnecessary but may help distinguish a parainfluenza virus infection from a bacterial infection in patients with severe lower respiratory tract disease. The virus can be detected by polymerase chain reaction, usually using a multiplex panel of common respiratory pathogens.
Treatment of parainfluenza virus infection is symptomatic.