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  • Bronchiolitis is a self-limited, virally mediated, acute inflammatory disease of the lower respiratory tract, resulting in obstruction of the small airways that occurs almost exclusively in infants.
  • It is a clinical diagnosis characterized by rapid respiration, chest retractions and wheezing, and, frequently, hypoxia.
  • Respiratory failure may occur secondary to respiratory muscle fatigue or apnea, especially in very young and premature infants.
  • Treatment is largely supportive. Routine treatment with bronchodilators or corticosteroids has not been shown to be of benefit.
  • Indications for hospital admission include need for supportive care (oxygen or IV fluids), persistent respiratory distress or respiratory failure, adjusted age <6 weeks, or significant underlying disease.


Bronchiolitis is a disease of the very young and occurs almost exclusively in children younger than 2 years. An attack rate of 11.4% in the first year of life and 6% in the second year of life was reported from one center. It is most common between the ages of 2 and 6 months. In the United States, it is the leading cause of hospitalization in infancy. It is the cause of more than 100 000 hospital admissions per year, which represents 17% of all hospitalizations of infants and an annual cost of more than $500 million.1,2 It is more common in males than females and has a seasonal pattern, being most common in the winter and spring.3


Bronchiolitis is an acute inflammatory disease of the lower respiratory tract that is characterized by acute inflammation, edema and necrosis of epithelial cells lining small airways, increased mucus production, and bronchospasm.4 The term is used to describe a clinical syndrome that occurs in infancy and is characterized by rapid respiration, chest retractions and wheezing, and, frequently, hypoxia.


The most common etiologic agent in bronchiolitis is respiratory syncytial virus (RSV). RSV is responsible for 70% of all bronchiolitis cases and for 80% to 100% of cases in winter months. Parainfluenza, adenovirus, and influenza account for most of the remaining cases.5 Infection with RSV does not grant permanent or long-term immunity. Reinfections are common and may be experienced throughout life.6 Other viruses that are known to cause bronchiolitis are mumps, echovirus, and rhinovirus. Mycoplasma pneumoniae and Chlamydia trachomatis have also been associated with bronchiolitis. Mycoplasma has been shown to be the principal agent in school-age children with bronchiolitis. Adenovirus is associated with a particularly severe form of bronchiolitis that can lead to a chronic condition known as bronchiolitis obliterans.


Infection produces inflammation of the bronchiolar epithelium, which leads to necrosis, sloughing, and luminal obstruction. Ciliated epithelium that has sloughed is replaced by cuboidal cells without cilia. Increased mucus production and edema contribute further to airway obstruction. The absence of ciliated epithelium prevents adequate mobilization of secretions and debris. Histologic sections of the tracheobronchial tree of patients with bronchiolitis are very similar to those in asthmatics. The bronchioles and small bronchi are obstructed secondary to the submucosal edema, peribronchiolar cellular infiltrate, mucous plugging, ...

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