The peak incidence is between two and six months of age, and over 80 percent of cases occur in the first year of life. After several days of coryza and fever, patients experience acute respiratory distress, wheezing, cough, and, often, inspiratory rales. In mild cases, symptoms resolve within several more days, although prolonged disease occurs in premature infants or patients with underlying cardiopulmonary disorders. The major differential diagnosis is asthma, which is uncommon in those younger than one year. The syndrome relates to viral destruction of the respiratory epithelium and associated peribronchiolar mononuclear inflammation, perhaps in part immunologically mediated, in the setting of disproportionately narrow airways.
Bronchiolar obstruction causes distal collapse or air trapping and abnormal gas exchange.
Correction of hypoxemia is the most important aspect of managing RSV bronchiolitis. Bronchodilators, glucocorticoids, and routine antibiotics are not of proven value. Aerosolized ribavirin therapy is available for infants hospitalized with RSV bronchiolitis or pneumonia, but it remains an expensive intervention of uncertain value. The relative importance of different viruses depends heavily on the season, age, and immune status. Influenza A and, less often, B viruses are the most common cause of viral pneumonia in community adults and account for over one half of documented cases of viral pneumonia.