Bronchiolitis is a topic covered in the 5-Minute Clinical Consult.

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  • Inflammation and obstruction of small airways and reactive airways generally affecting infants and young children—upper respiratory infection (URI) prodrome followed by increased respiratory effort, crackles, and wheezing
  • Usual course: insidious, acute, progressive
  • Leading cause of hospitalizations in infants and children in most Western countries
  • Predominant age: newborn—2 years (peak age <6 months). Neonates are not protected despite transfer of maternal antibody.
  • Predominant sex: male > female


  • There is a 21–25% prevalence of bronchiolitis (<12 months of age, 13% 12 to 24 months) in the United States and it accounts for ~$1.7B in health care cost in United States. Incidence is estimated at 3.2/1,000. Almost 100% of children experience RSV infection by two seasons.
  • Usually seasonal (October to May in the Northern Hemisphere) and often occurs in epidemics—in subtropical regions, RSV is endemic year-round
  • Responsible for 18.8% (90,000 annually) of all pediatric hospitalizations (excluding live births) in children <2 years
  • Incidence increasing since 1980 (with concomitant increase in relative rate of hospitalization from 2002 to 2007); of those <12 months with condition, the hospitalization rate ~2–3%

Etiology and Pathophysiology

RSV accounts for 70–85% of all cases (children <12 months of age), but rhinovirus, parainfluenza virus, adenovirus, influenza virus, Mycoplasma pneumoniae, and Chlamydophila pneumoniae have all been implicated:

  • Infection results in necrosis and lysis of epithelial cells and subsequent release of inflammatory mediators.
  • Edema and mucus secretion, which combined with accumulating necrotic debris and loss of cilia clearance, result in airflow obstruction.
  • Ventilation–perfusion mismatching resulting in hypoxia
  • Air trapping is caused by dynamic airways narrowing during expiration, which increases work of breathing.
  • Bronchospasm appears to play little or no role.

Risk Factors

  • Secondhand cigarette smoke
  • Low birth weight, premature birth
  • Immunodeficiency
  • Formula feeding (little or no breastfeeding)
  • Contact with infected person (primary mode of spread)
  • Children in daycare environment
  • Congenital cardiopulmonary disease
  • <12 weeks of age

General Prevention

  • Hand washing or use of alcohol-based hand rubs (preferred)—this simple exercise has been estimated to have the largest impact on prevention of transmission.
  • Contact isolation of infected babies
  • Persons with colds should keep contact with infants to a minimum.
  • Breastfeeding of infants has been associated with reduced morbidity of disease.
  • Palivizumab (Synagis), a monoclonal product, administered monthly, October to May, 15 mg/kg IM; used for RSV prevention ONLY in high-risk patients (see American Academy of Pediatrics [AAP] recommendations)

Pediatric Considerations
Prior infection does not seem to confer subsequent immunity.

Commonly Associated Conditions

  • Upper respiratory congestion
  • Conjunctivitis
  • Pharyngitis
  • Otitis media
  • Diarrhea

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