Bronchiolitis Causes and Risk Factors

Respiratory syncytial virus (RSV) causes approximately 85 percent of all bronchiolitis cases. RSV is highly contagious and can be spread quickly through physical contact (e.g., kissing, shaking hands) or through contact with an object (e.g., table, tissue, toy) that an infected person has touched.

RSV can survive for 30 minutes on a person's hands and for as many as 5 hours on objects (e.g., cups, doorknobs, telephones). It can become airborne when an infected person sneezes, coughs, or laughs, and usually enters the body through the eyes or nose. In most cases, children are infected by family members, friends, or children who attend the same daycare.

Although RSV causes most cases of bronchiolitis, other viruses and bacteria also can cause the condition. These pathogens (disease-causing organisms) include the following:

  • Adenoviruses (viruses that cause the common cold and also can affect the gastrointestinal [GI] tract; tend to cause severe symptoms)
  • Chlamydia pneumoniae (also can cause lung infection [pneumonia])
  • Parainfluenza viruses (usually occur early in the year and every other year)
  • Human metapneumovirus (infection may not cause symptoms)
  • Mycoplasma pneumoniae (also can cause lung infection [pneumonia])
  • Enteroviruses (e.g., coxsackievirus)
  • Rhinovirus (frequent cause for the common cold)

There are several risk factors associated with bronchiolitis. Infants younger than 6 months old, children who live in or visit crowded areas, children who are exposed to cigarette smoke (i.e., second-hand smoke), and children who have been bottle fed exclusively are at increased risk for bronchiolitis.

Premature infants (i.e., babies born more than 3 weeks before their due date), babies who have heart or lung disease, and babies with weakened immune systems have a higher risk for developing more serious cases of bronchiolitis.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 27 Aug 2008

Last Modified: 03 Sep 2015