Bronchiolitis is an infection that affects the lower respiratory tract of infants and young children under 24 months of age.

• Bronchiolitis usually is caused by viruses.
• Symptoms include runny nose, fever, cough, wheezing, and difficulty breathing.
• The diagnosis is based on symptoms and a physical examination.
• Most children do well at home and recover in a few days, but some need to be hospitalized.
• Treatment is primarily supporting the child through the illness with fluids and occasionally with oxygen.

Bronchiolitis is most often caused by respiratory syncytial virus and parainfluenza 3 virus, although other viruses, such as influenza, other forms of parainfluenza, metapneumovirus, and adenoviruses, are sometimes involved. Rare causes include rhinoviruses, enteroviruses, measles virus, and the bacteria Mycoplasma. Infection with these viruses causes inflammation of the airways. The inflammation causes the airways to narrow, obstructing the flow of air into and out of the lungs.

Bronchiolitis typically affects children younger than 24 months of age and is most common among 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 are affected. Most cases occur between November and April, with a peak incidence during January and February. The infection may be more common among infants whose mothers smoke cigarettes, particularly those who smoked during pregnancy. The infection seems to be less common among breastfed infants. Parents and older siblings can be infected with the same virus, but for them the virus usually causes only a mild cold.

Symptoms and Diagnosis

Bronchiolitis starts with symptoms of a cold—runny nose, sneezing, mild fever, and some coughing. After several days, children develop difficulty breathing, with an increase in respiratory rate and a worsening cough. Usually children have a high-pitched sound on breathing out (wheezing). In most infants, the symptoms are mild. Even though infants may breathe somewhat rapidly and be very congested, they are alert, happy, and eating well. More severely affected infants breathe rapidly and shallowly, use a lot of their respiratory muscles to breathe, and have flaring of their nostrils. They seem fussy and anxious and can become dehydrated because of vomiting and difficulty with drinking. A fever usually is present but not always. Some children also develop an ear infection. Premature infants or infants younger than 2 months sometimes stop breathing temporarily. In very severe and unusual cases, the child may become blue around the mouth caused by a lack of oxygen.

A doctor bases the diagnosis on the symptoms and the physical examination. Sometimes the doctor swabs mucus from deep inside the nose to try to identify the virus in the laboratory. Other laboratory tests may be done, and sometimes a chest x-ray is needed.

Prognosis and Treatment

Most children recover at home in 3 to 5 days. During the illness, frequent small feedings of clear fluids may be given. Wheezing and cough may continue for 2 to 4 weeks. Increasing difficulty in breathing, bluish skin discoloration, fatigue, and dehydration indicate that the child should be hospitalized. Children with congenital heart or lung disease or an impaired immune system may be hospitalized sooner and are far more likely to become quite ill from bronchiolitis. With proper care, the chance of developing serious consequences due to bronchiolitis is low, even for children who need to be hospitalized.

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Some children have repeated episodes of wheezing after having had bronchiolitis.

Most children can be treated at home with fluids and comfort measures. In the hospital, oxygen levels are monitored with a sensor attached to a finger or toe, and oxygen is given by an oxygen tent or face mask. A ventilator may be needed to assist breathing. Fluids are given by vein if the child cannot drink adequately. Inhaled drugs that open the airways (bronchodilators) may be tried, although their effectiveness in treating bronchiolitis is questionable. The antiviral drug ribavirin given by nebulizer is no longer given routinely but may be given to infants who are premature or who have other conditions that put them at high risk of severe breathing problems, such as congenital heart or lung disease, cystic fibrosis, or AIDS. Antibiotics are not helpful.

Last full review/revision February 2009 by Anand D. Kantak, MD; John T. McBride, MD