Parainfluenza viruses are a family of single-stranded enveloped RNA viruses that are a common cause of upper and lower respiratory illnesses, most often seen in children. The family is divided into 5 subtypes; type 3 is the most common. By the age of 5 most children have experienced parainfluenza infection. Parainfluenza can be spread via direct person-to-person contact or large droplet inhalation and has an incubation period ranging from 2 to 6 days. In healthy children, parainfluenza is responsible for mild upper respiratory tract illnesses, otitis media, bronchiolitis, croup, and occasionally interstitial pneumonitis and pneumonia. In immunocompetent adults, clinically it usually appears as a mild, self-limited upper respiratory tract infection, although it can also lead to community-acquired pneumonia. Parainfluenza is also linked to asthma and chronic obstructive pulmonary disease exacerbations and rarely with aseptic meningitis and Guillain-Barré syndrome.

In elderly, HIV-positive, and immunocompromised individuals, including adult and pediatric solid organ transplant (SOT) recipients, hematopoietic stem cell transplant (HSCT) recipients, and patients with primary immunodeficiency, parainfluenza can cause severe upper respiratory tract illnesses along with pneumonia and interstitial pneumonitis, which can be fatal.

Symptoms:

• Cough, often barking
• Hoarseness
• Wheezing
• Rhinorrhea
• Sore throat

Signs:

• Rales/rhonchi
• Fever above 38°C (100.4°F)
• Irritability
• Stridor
• Dyspnea

Risk factors for severe disease:

• Infants
• T-cell immune defects (SOT, HSCT, and primary immunodeficiencies)

Note: In 2022 and 2023, pediatric invasive group A streptococcal (iGAS) infections and noninvasive group A streptococcal infection cases have been associated with respiratory infections due to parainfluenza among other viruses. Concurrent or preceding viral infections, including varicella (chickenpox), may increase risk for iGAS infection. Severe outcomes of iGAS infections include necrotizing fasciitis, streptococcal toxic shock syndrome, and death.