There are four types of Parainfluenza virus, all of which can cause upper respiratory infections or lower respiratory infections (pneumonia) in adults and children. The virus is especially important in children because it is responsible for approximately 40-50% of croup cases and 10-15% of bronchiolitis and bronchitis cases and some pneumonias. The exact number of cases of parainfluenza is unknown but suspected to be very high. Sometimes the viruses cause only a runny nose and other symptoms that may be diagnosed as a simple cold rather than parainfluenza. Risk factors for parainfluenza include young age. By school age, most children have been exposed to parainfluenza virus. Most adults have antibodies against parainfluenza although they can get repeat infections.
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