Viral infections of the respiratory tract lower

Viral infections of the lower respiratory tract are very common in children, especially during the first three years of life. Most respiratory viral infections show a predominant seasonal incidence during the cold months of the year. Viral respiratory tract infections are generally not serious, since only cause deaths in young children with heart or respiratory basis; however, they are a frequent cause of medical care and hospitalization, especially respiratory syncytial virus infections in infants and seasonal influenza disease each winter. Respiratory viruses are the cause of the two major clinical syndromes in the lower airways: bronchiolitis and pneumonia, with existence of overlapping and mixed or intermediate features between each other and with occasional involvement of the larynx and trachea (Table I). None of these clinical conditions is associated with a single respiratory virus, although each clinical presentation is clearly related to one or more etiologic agents.