by Caroline B. Hall, M.D.
Professor of Pediatrics, University of Rochester School of Medicine and Dentistry Rochester, New York

What is bronchiolitis?

Bronchiolitis is an infectious disease of the lower respiratory tract caused by a virus. It occurs in young children, usually within the first two years of life. Signs of an upper respiratory tract infection (a "cold"), as well as signs of a lower respiratory tract infection, characterized by wheezing, commonly accompany bronchiolitis. For this reason, bronchiolitis has sometimes been called "asthmatic bronchitis" or "wheezy bronchitis."


What causes bronchiolitis?

Respiratory viruses cause bronchiolitis. Many common viruses, especially those that occur in the winter and spring, may cause bronchiolitis in young children. The most frequent cause of bronchiolitis is Respiratory Syncytial Virus (RSV). RSV causes outbreaks of bronchiolitis each year throughout most of the world. In North America, RSV causes regular outbreaks, lasting two to three months, which begin in the late fall or winter, and varying somewhat depending on the area of the country. In the warmer parts of the United States, the annual outbreaks tend to start slightly earlier than in the colder, more northern climates, which usually experience the beginning of an outbreak in November or December, with peak activity in January through March. Parainfluenza viruses, the second most common cause of bronchiolitis, also tend to occur in outbreaks, but at different seasons. Parainfluenza type 1 virus produces outbreaks in the fall every other year in the odd numbered years, while parainfluenza type 3 virus-which is the most common of the parainfluenza viruses to cause bronchiolitis-is prominent in the spring, but may last into the summer and fall. Occasionally, influenza also may cause bronchiolitis in young children during its winter to spring outbreaks. A number of other common viruses that cause respiratory infections, especially colds, may sometimes cause bronchiolitis in the young child. These respiratory viruses that cause the majority of bronchiolitis cases have two common characteristics: first, they are widespread viruses, which infect essentially all of us early in life and, sometimes, repeatedly throughout life. Second, these viruses each cause multiple types of respiratory illness, including upper respiratory tract infections, such as colds and ear infections, as well as infections of the lower respiratory tract, such as pneumonia, bronchitis, and laryngitis.


Who gets bronchiolitis?

Bronchiolitis is a common illness occurring in normal children during their first or second year of life, most frequently between 2 and 10 months of age. Younger infants and those who were born prematurely tend to have more severe illness. Children who are in day care during their first year of life are frequently exposed to respiratory viruses from their close contact with many other young children; therefore, they often have many respiratory infections during their first year. RSV spreads easily among groups of young children, and, in some, it may appear as bronchiolitis, while, in others, it may appear only as an upper respiratory tract infection. Children who are infected with RSV or with another of the bronchiolitis viruses may even become infected again in their second year of life with the same virus.


How do respiratory viruses cause disease?

The respiratory viruses that cause bronchiolitis are acquired from close contact with other individuals who are infected with the virus. Sometimes, these people show signs of illness, and, at other times, the infection may be very mild with few or no symptoms. The viruses, nevertheless, are still present in the secretions, and they are infectious when they enter the respiratory tract of a child via the eyes, nose, or, occasionally, the mouth. The spread of these viruses from individuals who are infected usually occurs from the small particles of respiratory mucus that are released from their sneezes or from touching their secretions that may be on used tissues or on other objects. When children rub their eyes or nose with hands contaminated by these secretions, the virus may enter the respiratory tract. In the lining of the nose and the upper respiratory tract, the virus multiplies and spreads down to the lower airways and lungs. During the initial few days, when the virus is multiplying, the child usually does not show any symptoms. Subsequently, however, the virus causes damage to the cells lining the respiratory tract, resulting in an excess of cellular material and secretions, which tend to obstruct the usual flow of air. Young infants are particularly vulnerable to this "plugging effect" because the diameter of their airways is small. The obstruction to their breathing tends to be most pronounced when they are exhaling, as the diameter of the airway is reduced more during the increased pressure needed for breathing out. A wheezy sound may be heard as the child forces the air through these areas of partial obstruction.


What are the common findings in a child with bronchiolitis?

Initially, bronchiolitis appears as an upper respiratory tract infection (i.e., a cold), with nasal stuffiness, a sore throat, and a slight cough. Fever, which is usually mild, but, occasionally, may be high, is frequent during these initial few days of the infection. Involvement of the lower respiratory tract usually appears two to three days later, and is characterized by the child developing a more prominent cough and the general signs of a worsening infection, such as irritability, decreased activity, and poor appetite. If the infection progresses further, the child may seem to have labored, fast, or wheezy breathing. The child may grunt with the effort of each breath, and the child's chest muscles may retract between the ribs. Only the more severely ill children have labored breathing; most appear to have a bad cold with wheezy or croupy breathing. Whenever parents are concerned about a change in the sound, effort, or pattern of their child's breathing, they should call their physician. For most infants, bronchiolitis lasts three to seven days. Although most show improvement within three to four days, a more prolonged cough and a gradual recovery period of one to two weeks or longer is common.


How is bronchiolitis diagnosed?

Bronchiolitis is diagnosed most frequently on its characteristic appearance in a child of the right age, especially when it occurs during the RSV season. For instance, a child within the first two years of life who develops a cold and wheezing during the winter months of peak RSV activity in a community is most likely to have bronchiolitis. Several other diseases, however, may appear similar to bronchiolitis. Asthma cannot always be easily differentiated from bronchiolitis, particularly if the child is having the first episode of wheezing. Furthermore, the two diseases may be combined since a significant proportion of wheezing episodes occurring in allergic or asthmatic children are initiated by a virus. Young children who have repeated episodes of bronchiolitis or wheezing are more likely to have asthma or an allergic background. Occasionally, the repetitive episodes of wheezing may be due to gastric reflux, a condition resulting from the tendency of some young infants to regurgitate stomach contents in the respiratory tract after feeding. Rarely, a child swallowing or choking on something that lodges in the respiratory tract and causes an obstruction of the airway will mimic bronchiolitis. The child's physician may sometimes wish to get a chest x-ray or a measurement of the oxygen level in the blood to help confirm the diagnosis or severity of bronchiolitis. Secretions from the nose and throat may be tested for the presence of the respiratory virus causing bronchiolitis.


How is bronchiolitis treated?

The vast majority of children with bronchiolitis do well with no more than the usual care required for an infant with a bad cold. If fever is present, the usual medications to control it, such as acetaminophen and ibuprofen, should be used. The child should be encouraged to take an adequate amount of fluids. Solid food is less important. Alleviating the nasal stuffiness may help the child in taking fluids and in sleeping. Saline nose drops or other mild drops and suctioning, as advised by your physician, may help. Sometimes, a cold water humidifier in the child's room may aid the nasal stuffiness caused by thick, dried secretions. In the more severely ill child with the signs of lethargy and difficulty in breathing, hospitalization may be required to administer additional oxygen or fluids if the child is dehydrated. Since a virus causes bronchiolitis, the antibiotics used for bacterial infections, such as strep throats and ear infections, are of no benefit. Viruses do not respond to such antibiotics. Currently, only one antiviral drug is approved for use for bronchiolitis caused by RSV. This drug, ribavirin, can be administered in a hospital by an aerosol into the child's nose and mouth. Some children may be treated with bronchodilator drugs, which are aimed at reducing the airway obstruction, which occurs in some children, mainly those with allergies. Many infants with bronchiolitis, however, do not respond or have a variable response to bronchodilators. In most young infants, the major cause of the airway obstruction is the inflammation caused by the virus, rather than an abnormal reaction of the child's airways. Corticosteroids have been evaluated in the treatment of bronchiolitis in an attempt to reduce the inflammation. However, carefully controlled studies have shown that they have no benefit in treating bronchiolitis, and the American Academy of Pediatrics does not advise the use of these drugs for bronchiolitis.


What are the complications?

Many studies of large numbers of children with bronchiolitis have shown that those infants who were most likely to have a complicated or severe case are those with underlying diseases, especially heart or lung disease. Additionally, those children who were born prematurely and those infants in the first few weeks of life are more at risk for prolonged or complicated illnesses. Infants who have the most severe illness may have such difficulty in breathing that they require assistance in their breathing with mechanical ventilation. Very young infants may have the complication of suddenly stopping breathing for prolonged periods, called apnea. Such complications are generally rare, and the death rate from bronchiolitis is very low. The most common complication of bronchiolitis for children hospitalized with a more severe infection is recurrent episodes of wheezing within the first two years after discharge from the hospital. However, over the years, the frequency of these continued episodes of wheezing tends to decrease markedly. Most studies show that children who have had milder bronchiolitis, not requiring hospitalization, do not have this same degree of risk for recurrent episodes of wheezing.


How can bronchiolitis be prevented?

For most children, currently, there is not an effective way to prevent bronchiolitis. Since several very common respiratory viruses, especially RSV, cause bronchiolitis, contact with others who are infected is frequent and often is not recognized. Within the child's family, spread of RSV and other respiratory viruses may be lessened by good hand-washing of the parents and other family members and by reducing an infant's contact with secretions from an infected person (e.g., contaminated used tissues, shared toys, utensils, and other objects). Isolation of the child and interference with the child's usual play and activities are usually of little value and should not be attempted for most normal children. For those few infants who are at a very high risk for complicated or severe infections from RSV, namely those who were born with significant prematurity and/or underlying lung disease, an additional means of prevention is available. A product containing a specific antibody to RSV has been approved for monthly administration to help prevent RSV infection in these high-risk children. This form of antibody against RSV has the advantage of being able to be administered once a month by intramuscular injection. In large, controlled studies, this product has been shown to decrease hospitalization from RSV infections in these high-risk infants.


What research is being done?

Since these respiratory viruses, especially RSV, produce so much illness in young children and are a major cause of medical visits and costs, much research currently is underway. This research is focused on developing effective vaccines to prevent RSV and to prevent infection with some of the other respiratory viruses, such as the parainfluenza and influenza viruses. Although a number of vaccines for the prevention of RSV have been tested in clinical trials, they have yet to be approved for general use. A number of vaccines, which contain live, but weakened, or inactive parts of the virus, appear promising and are being tested further. In addition, a number of antiviral drugs are being developed and tested for both preventing and treating the viruses that cause bronchiolitis.



Gruber WC: Bronchiolitis: In Long SS, Pickering LK, Prober CG, eds. Principles and Practices of Pediatric Infectious Diseases, 2nd edition, 1997: 246. * Hall CB, Hall WJ: Bronchiolitis. In: Mandell GL, Benett JE, Dolin R, eds. Principles and Practice of Infectious Diseases, Fifth Edition. New York, NY: Churchill Livingstone Inc. 1999 (in press). * Hall CB, Hall WJ: Bronchiolitis. In: Hoekelman RA, Friedman SB, Nelson NM, Seidel HM, Weitzman ML ed. Primary Pediatric Care. Fourth Edition. St. Louis, MO: C.V. Mosby 1999 (in press). * These two references are also currently in the published editions: Hall CB, Hall WJ: Bronchiolitis. In: Mandell GL, Benett JE, Dolin R, eds. Principles and Practice of Infectious Diseases, Fourth Edition. New York, NY: Churchill Livingstone Inc. 1994:612-614. Hall CB, Hall WJ: Bronchiolitis. In: Hoekelman RA, Friedman SB, Nelson NM, Seidel HM, Weitzman ML ed. Primary Pediatric Care. Third Edition. St. Louis, MO: C.V. Mosby 1997:1213-1216.

About the Author

Dr. Hall is board certified in pediatrics and the subspecialty of pediatric infectious diseases. She is also a Professor of Pediatrics and Medicine at the University of Rochester Medical Center. She has served on a number of national and government committees concerning infectious diseases and immunizations. Her major areas of medical research concern viral diseases of children, especially respiratory viruses, as well as other viral infections, such as HHV6 and HHV7, immunizations and epidemiology. Reviewed 11/3/2010

Copyright 2012 Caroline B. Hall, M.D., All Rights Reserved