Bronchiolitis is a common illness of the respiratory tract caused by a respiratory infection that affects the tiny airways, called the bronchioles, that lead to the lungs. As these airways become inflamed, they swell and fill with mucus, making it difficult for a child to breathe.
The illness affects infants and young children most often because their small airways can become blocked more easily than those of older children or adults. Bronchiolitis typically occurs during the first 2 years of life, with the peak occurrence at about 3 to 6 months of age. It’s more common in males, children who have not been breastfed, and children who live in crowded conditions. Day-care attendance and exposure to cigarette smoke can also increase the likelihood that an infant will develop bronchiolitis.
Although it’s often a mild illness, some infants are at risk for a more severe disease that requires hospitalization. Conditions that increase the risk of severe infection include prematurity, prior chronic heart or lung disease, and a weakened immune system due to illness or medications. Children who have had bronchiolitis may be more likely to develop asthma later in life, but it’s unclear whether bronchiolitis causes or triggers asthma, or whether children who eventually go on to develop asthma were simply more prone to developing bronchiolitis as infants. Studies are being done to clarify the relationship between bronchiolitis and the later development of asthma.
Bronchiolitis is usually caused by a viral infection, most commonly respiratory syncytial virus. RSV infections are responsible for more than half of all cases of the illness and are most widespread in the winter and early spring. Other viruses associated with bronchiolitis include influenza and adenovirus.
Signs and Symptoms
The first symptoms of bronchiolitis are usually the same as those of a common cold:
- runny nose
- mild cough
These symptoms last a day or 2 and are followed by worsening of the cough and the appearance of wheezes (high-pitched whistling noises when breathing out).
Sometimes more severe respiratory difficulties gradually develop, marked by:
- rapid, shallow breathing (60 to 80 times a minute)
- a rapid heartbeat
- drawing in of the neck and chest with each breath, known as retractions
- flaring of the nostrils
- irritability, with difficulty sleeping and signs of fatigue
The child may also have a fever, a poor appetite, and may vomit after coughing. Less commonly, young infants, especially those born prematurely, may have episodes where they briefly stop breathing (this is called apnea) before developing other symptoms.
In severe cases, symptoms may worsen quickly. A child with severe bronchiolitis may tire from the work of breathing and have poor air movement in and out of the lungs, due to the clogging of the small airways. The skin can turn blue (called cyanosis), which is especially noticeable in the lips and fingernails. The child can also become dehydrated from working harder to breathe, vomiting, and taking in less during feedings.
The infections that cause bronchiolitis are contagious. The germs can spread in tiny drops of fluid from an infected person’s nose and mouth. These may become airborne when the person sneezes, coughs, or laughs, and they may also end up on things the person has touched, such as used tissues or toys.
Infants in child-care centers have a higher risk of contracting an infection that may lead to bronchiolitis because they’re in close contact with lots of other young children.
The best way to prevent the spread of viruses that can cause bronchiolitis is frequent hand washing. It may help to keep infants away from others who have colds or coughs. Infants who are exposed to cigarette smoke are more likely to develop more severe bronchiolitis, compared to babies from smoke-free homes. Therefore, it’s important to avoid exposing children to cigarette smoke.
Although a vaccine for bronchiolitis has not yet been developed, there is a medication that can be given to lessen the severity of the disease. It consists of antibodies to RSV and is injected monthly during peak RSV season. The medication is recommended only for infants at high risk of severe disease, such as those born very prematurely or those with chronic lung disease.
The incubation period (the time between infection and the onset of symptoms) ranges from several days to 1 week, depending on the infection that leads to the bronchiolitis.