What is bronchiolitis?Bronchiolitis is an infection of the lower respiratory tract that usually affects infants. There is swelling in the smaller airways or bronchioles of the lung, which causes obstruction of air in the smaller airways. Bronchiolitis is almost always caused by a virus, most commonly the respiratory syncytial virus (RSV). Other viruses that can cause this condition are parainfluenza,
influenza, measles, and adenovirus. The infection causes inflammation and swelling of the bronchioles, which in turn, blocks the airflow through the lungs.
Bronchiolitis begins as a mild upper respiratory infection that, over a period of 2 to 3 days, can develop into increasing respiratory distress with wheezing and a "tight", wheezy cough. The infant's breathing rate may increase markedly (tachypnea), and the infant may become irritable or anxious-looking. If the disease is severe enough, the infant may turn bluish (cyanotic), an indication of a critical emergency. As the effort of breathing increases, parents may see the nostrils flaring with each breath and the muscles between the ribs retracting (intercostal retractions) as the child tries to inhale air. This can be exhausting for the child, and very young infants may become so fatigued that breathing becomes difficult to maintain.
Bronchiolitis typically affects children younger than 18 months of age and is most common in infants younger than 6 months. During the first year of life, bronchiolitis affects about 11 of every 100 children, although during some epidemics a much higher proportion of infants is affected. Bronchiolitis is seasonal and appears more frequently in the fall and winter months. It is a very common reason for infants to be hospitalized during winter and early spring. Some children have subclinical infections, that is, few or insignificant symptoms. It is estimated that by the first year, more than half of all infants have been exposed to RSV.