Human Parainfluenza Type 4 Infections, Canada

H parainfluenza viruses (HPIVs) have been recognized as a cause of respiratory tract infections for many decades. They belong to the Paramyxoviridae family, subfamily Paramyxovirinae, and are classified into 4 serotypes. Serotype 4 can be further subdivided into 2 antigenic subtypes, HPIV-4A and HPIV-4B (1). Although the epidemiology and clinical manifestations of serotypes HPIV-1 to HPIV-3 are well described, much less is known about HPIV-4, including its seasonality (2). HPIV-4 has been mostly associated with mild illnesses (3,4). However, some evidence has indicated that it can cause more severe infections in some settings (5–10). We sought to describe the virologic and molecular characteristics as well as the clinical manifestations associated with HPIV-4 infections at our hospital during 2004–05.