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