Parainfluenza Virus Infections

The parainfluenza viruses are paramyxoviruses. They are classified as types 1, 2, 3, and 4. They share antigenic cross-reactivity but usually 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 infection can occur in nurseries, pediatric wards in hospitals, and schools (1). Types 1 and 2 typically cause epidemics in autumn, with each type occurring in alternate years. Type 3 disease is endemic and infects most children < 1 year; incidence is increased in spring and early summer.

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. All viral types are common triggers of chronic underlying lung conditions (eg, asthma exacerbations). Parainfluenza viruses can also cause disease in immunocompromised and older adults.

Parainfluenza virus type 1 is a frequent cause of croup (laryngotracheobronchitis), primarily in children aged 6 to 36 months (1, 2). 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 virus 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.

Parainfluenza virus type 4 can cause mild to severe respiratory tract illness, including bronchiolitis and pneumonia; however, it is diagnosed less often because of infrequent testing.

Diagnostic confirmation of parainfluenza virus infection is usually 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 (PCR) testing, usually using a multiplex panel of common respiratory pathogens (3).

The treatment of parainfluenza virus infection is primarily symptomatic. There are no commercially available vaccines that protect against parainfluenza virus infections.