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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 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% incidence of bronchiolitis in the United States and it accounts for ~$1.7B in health care cost in United States.
- May be seasonal (October to May in the Northern Hemisphere) and often occurs in epidemics
- 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.
- Secondhand cigarette smoke
- Low birth weight, premature birth
- 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
- Hand washing or use of alcohol-based hand rubs (preferred)
- 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)
Prior infection does not seem to confer subsequent immunity.
Commonly Associated Conditions
- Upper respiratory congestion
- Otitis media