Human parainfluenza virus (HPIVs) is a virus that frequently causes lower respiratory tract infections in children, second only to respiratory syncytial virus (RSV) in pathogenicity. Like RSV, human parainfluenza viruses can cause recurrent upper respiratory infections (such as colds and sore throats). It can also cause severe recurrent lower respiratory diseases (such as pneumonia, bronchitis and bronchiolitis), especially in the elderly and in people with immune deficiencies.