Human parainfluenza viruses types 1, 2, and 3 (HPIV-1, HPIV-2, and HPIV-3) are the second most common causes of lower respiratory tract disease in infants and young children. Parainfluenza 1 and 2 are the leading causes of croup, and parainfluenza type 3, like RSV, is an important cause of bronchiolitis and pneumonia in young infants. Most children are infected by HPIV-3 by the age of two years and by HPIV-1 and HPIV-2 by the age of five years. HPIV-1 is estimated to account for 16,300 to 96,500 annual hospitalizations in the US. Along with RSV, parainfluenza viruses are also leading causes of hospitalization in adults with community-acquired respiratory disease.
National Center for Infectious Diseases, Respiratory and Enteric Viruses Branch
Initiative for Vaccine Research