Bronchiolitis is a clinical diagnosis preceding upper respiratory illness and/or rhinorrhea.
Signs of respiratory illness which may include wheezing, retractions, oxygen desaturation, color change, nasal flaring.
There is also presence of apnea especially in premature or low birthweight infants, signs of dehydration and exposure to persons with viral upper respiratory infections.
Symptoms are usually worst on the 3rd-5th day of illness and then improve gradually.


  • Bronchiolitis is a disease of the lower respiratory tract characterized by acute inflammation & edema of the bronchioles, accompanied by increased mucus production
  • Usually affects children <2 years of age
  • Among the leading causes of hospitalization of infants in the United States and Asia


  • Majority of cases are caused by the respiratory syncytial virus (RSV)
  • Other etiologic agents include rhinovirus, adenovirus, parainfluenza, Mycoplasma
  • There is no evidence of bacterial etiology for bronchiolitis, but bacterial superinfection may occur
    • Otitis media is the most common bacterial infection associated w/ bronchiolitis
  • Epithelial necrosis, mucus hypersecretion, round-cell infiltration, and submucosal inflammation brought about by RSV infection causes bronchiolar narrowing, which leads to mucus plug formation, bronchiolar obstruction, and distal lung tissue overinflation, resistance, and collapse

Signs and Symptoms

  • Symptoms are usually worst on the 3rd-5th day of illness, & then improve gradually
  • Preceded by upper respiratory infections
  • Initially sneezing, mild rhinorrhea, nasal obstruction, cough
  • May progress to respiratory distress w/ wheezing, crackles, irritability, shortness of breath, tachypnea
    • Lower respiratory tract infection (mainly bronchiolitis & pneumonia) should be suspected w/ increased respiratory rate (RR)
  • Anorexia, fever (<39°C)
    • Other diagnosis should be considered 1st in the presence of axillary temperature of ≥39°C
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