Bronchiolitis (See Also: Respiratory Syncytial Virus)



Acute infection of the lower respiratory tract in infants and young children leading to mononuclear infiltration of the bronchiolar epithelium, causing edema and mucus plugging of the small airways


  • Peak season is November through April, with some variation by state in the United States (begins earlier in the Southeast).
  • Most common cause of infant hospitalization
    • ~150,000 hospitalizations per year in the United States
    • Hospitalization rates tripled from 1980 to 1997 with the advent of pulse oximetry but have decreased slightly over the last decade.
  • Most recent estimate ~15 hospitalizations per 1,000 person-years for children <2 years of age
  • Approximately 1/3 of all children will get bronchiolitis in the first 2 years of life.

General Prevention

  • Hand hygiene is the only preventative measure for otherwise healthy infants and children.
  • Palivizumab can be given to high-risk infants and young children (see “Respiratory Syncytial Virus” [RSV] section for discussion of RSV immunoprophylaxis).


  • RSV is the most common causative organism, but other organisms include the following:
    • Human rhinovirus
    • Adenovirus
    • Human metapneumovirus
    • Enterovirus
    • Coronaviruses
    • Influenza viruses
    • Parainfluenza viruses
    • Mycoplasma pneumoniae
    • Human bocavirus
  • Majority of bronchiolitis cases are caused by one virus, but viral coinfections (two or more viruses) may occur in ~1/4 of cases.

Risk Factors

  • Patients at high risk of severe bronchiolitis:
    • Premature infants (<36 weeks’ gestation)
    • Young infants (<2 to 3 months of age)
    • Congenital heart disease
    • Chronic lung disease (including bronchopulmonary dysplasia [BPD])
    • Low birth weight
    • Cystic fibrosis
    • Immunodeficiency
    • Neuromuscular diseases
    • Trisomy 21
  • Exposure to cigarette smoke is a risk factor for more severe disease.

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