Bronchiolitis

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Overview, Causes, & Risk Factors

The disease usually affects children under the age of 2, with a peak age of 3 to 6 months, and is a common, sometimes severe illness. Respiratory syncytial virus (RSV) is one common cause. Other viruses that can cause bronchiolitis include: parainfluenza, influenza, and adenovirus.

The virus is transmitted from person-to-person by direct contact with nasal secretions or by airborne droplets. Although RSV generally causes only mild symptoms in an adult, it can cause a severe illness in an infant.

Bronchiolitis begins as a mild upper respiratory infection that, over a period of 2 to 3 days, can develop into a condition of 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 as the child tries to inhale air. This can be exhausting for the child, and very young infants may simply fatigue to an extent that breathing becomes difficult to maintain.

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.

Risk factors include:

• Age (less than 6 months old)
• No history of being breastfed
• Prematurity (born before 37 weeks gestation)
• Exposure to cigarette smoke
• Crowded living conditions