DESCRIPTION

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.

EPIDEMIOLOGY

• Peak season
  • Typically, November through April, with some variation by state in the United States (begins earlier in the Southeast)
  • Of note, the COVID-19 pandemic changed the seasonality of bronchiolitis (see “Respiratory Syncytial Virus”).
• Most common cause of infant hospitalization
  • ~100,000 hospitalizations/year in the United States
  • Hospitalization rates have steadily increased over the last 15 years. Greater reliance on pulse oximetry may have lower the threshold for admission in patients with bronchiolitis.
• Most recent estimate ~15 hospitalizations/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.

ETIOLOGY

• RSV is the most common causative organism, but other organisms include the following:
  • Human rhinovirus
  • Adenovirus
  • Human metapneumovirus
  • Enterovirus
  • Coronaviruses
  • Influenza viruses
  • Parainfluenza viruses
• Majority of bronchiolitis cases are caused by one virus, but viral coinfections (2 or more viruses) may occur in ~1/4 of cases.

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” for discussion of respiratory syncytial virus [RSV] immunoprophylaxis).

COMMONLY ASSOCIATED CONDITIONS

• Patients at high risk for 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.