Bronchiolitis
Basics
Description
- Inflammation and obstruction of small airways and reactive airways generally affecting infants and young children; manifests as an upper respiratory infection (URI) prodrome followed by increased respiratory effort, crackles, and wheezing
- Usual course: insidious, acute, progressive with a variable duration; some experience persistent symptoms (primarily cough) for 14 to 21 days.
- Leading cause of hospitalizations in infants and children in most Western countries; it is the most common cause of lower respiratory tract infections (LRTI) in children <24 months of age.
- Predominant age: newborn to 2 years (peak age <6 months); neonates are not protected despite transfer of maternal antibody.
- Predominant sex: male > female
Epidemiology
Incidence
- Accounts for ~$1.7 billion in health care costs in the 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 aged <2 years
- Incidence is increasing since 1980 (with concomitant increase in relative rate of hospitalization from 2002 to 2007); of those <12 months of age with condition, the hospitalization rate is ~2–3%.
Prevalence
There is a 21–25% prevalence of bronchiolitis in children <12 months of age, decreasing to 13% from 12 to 24 months of age in the United States.
Etiology and Pathophysiology
RSV accounts for 70–85% of all cases (children <12 months of age), but rhinovirus, parainfluenza virus, metapneumovirus, adenovirus, influenza virus, Mycoplasma pneumoniae, and Chlamydophila pneumoniae have all been implicated (1):
- 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, which may result 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 (especially those infants born <35 weeks’ gestation)
- Immunodeficiency—both congenital and acquired
- Formula-fed infants
- Contact with infected person (primary mode of spread)
- Children in daycare environment
- Congenital cardiopulmonary disease
- Comorbid neurologic disorder
- <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 for at least 6 months 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) (2)
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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Citation
Domino, Frank J., et al., editors. "Bronchiolitis." 5-Minute Clinical Consult, 33rd ed., Wolters Kluwer, 2025. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688482/1.1/Bronchiolitis.
Bronchiolitis. In: Domino FJF, Baldor RAR, Golding JJ, et al, eds. 5-Minute Clinical Consult. Wolters Kluwer; 2025. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688482/1.1/Bronchiolitis. Accessed December 3, 2024.
Bronchiolitis. (2025). In Domino, F. J., Baldor, R. A., Golding, J., & Stephens, M. B. (Eds.), 5-Minute Clinical Consult (33rd ed.). Wolters Kluwer. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688482/1.1/Bronchiolitis
Bronchiolitis [Internet]. In: Domino FJF, Baldor RAR, Golding JJ, Stephens MBM, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2025. [cited 2024 December 03]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688482/1.1/Bronchiolitis.
* Article titles in AMA citation format should be in sentence-case
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