Acute Bronchiolitis

Acute bronchiolitis is a respiratory condition caused by inflammation of the bronchioles. The condition is a common cause of hospitalization in children in the United States, with the majority of cases caused by respiratory syncytial virus (RSV). Patients usually present with upper respiratory symptoms, such as cough and congestion, and later develop lower respiratory signs, including dyspnea, wheezing, crackles, and hypoxia, for up to 10 days. Diagnosis is clinical and treatment is directed at improving oxygenation and hydration. As the disease course is self-limiting, acute bronchiolitis has good prognosis with appropriate management.

Last update:

Table of Contents

Share this concept:

Share on facebook
Share on twitter
Share on linkedin
Share on reddit
Share on email
Share on whatsapp



Acute bronchiolitis is a clinical constellation of respiratory symptoms (increased work of breathing, wheezing, and crackles) caused by acute inflammation of the small airways (small bronchi and bronchioles), typically secondary to viral infections.


  • Population statistics:
    • Peak incidence between 2 and 6 months of age
    • Leading cause of hospitalization of infants in the United States
  • Seasonal preference (respiratory syncytial virus (RSV)–related): fall and winter 
  • Risk factors for severe disease:
    • Individual factors:
      • Prematurity (born < 37 weeks of gestation)
      • < 12 weeks of age
      • Low birth weight (< 2.5 kg)
      • Immunodeficiency
      • Congenital heart disease
      • Cystic fibrosis
      • Bronchopulmonary dysplasia (BPD)
    • Environmental factors:
      • Overcrowding (daycare or household)
      • Passive smoke inhalation
      • Contact with school-age siblings
      • Low socioeconomic status
      • Not breastfed
Seasonal behaviour of bronchiolitis

The annual distribution (%) of pathogens that cause bronchiolitis. “Bronchiolitis season” starts around October and finishes around May in the Northern Hemisphere.

Image by Lecturio.


  • Viral infection:
    • RSV: ⅓ of cases
    • Rhinovirus
    • Less common: 
      • Parainfluenza virus
      • Human metapneumovirus
      • Influenza virus
      • Adenovirus
      • Mycoplasma pneumoniae 
      • Pertussis
Causes of bronchiolitis

Seasonal variations in the number of cases that can be attributed to the respiratory syncytial virus (RSV): At its peak, RSV accounts for about ⅓ of bronchiolitis.

Image by Lecturio.

Pathophysiology and Clinical Presentation


Pathological changes are noted within 24 hours of contact with a pathogen:

  • Virus enters epithelial cells of terminal bronchioles.
  • Inoculation causes inflammation → edema, mucus secretion, and epithelium sloughing
  • Sloughing and edema → narrowing and obstruction of small airways
  • Narrowing results in atelectasis and symptoms begin to appear.

Clinical presentation

Symptoms are on a spectrum based on the severity of the disease:

  • Initial 1–3 days (upper respiratory tract symptoms):
    • Cough
    • Congestion
    • Rhinorrhea
  • Peaks on day 3–5, lasting up to 10 days (lower respiratory tract symptoms):
    • Wheezing and diffuse crackles on lung exam
    • Fever
    • Shortness of breath
  • Severe cases:
    • Apnea in infants, especially during sleep
    • Respiratory failure:
      • Tachypnea
      • Cyanosis
      • Nasal flaring
      • Grunting
      • Intercostal retraction
      • Hypoxia < 92% saturation

Diagnosis and Management


  • Diagnosis based on clinical suspicion: 
    • Characteristic lower respiratory tract symptoms
    • Patients < 2 years
    • Presenting during the fall and winter seasons
  • Further investigation: 
    • High fever
    • Severe presentation 
    • History of comorbidities
  • Routing testing of any kind is discouraged as it adds no additional therapeutic value.
  • Investigation in severe cases to evaluate comorbid conditions or superimposed infection:
    • Complete blood count (CBC): leukocytosis 
    • Chest X-ray: hyperinflation with atelectasis 
    • RSV testing on aspirate


Management depends on severity:

  • Mild-to-moderate cases → supportive:
    • Caregiver education on upright positioning during sleeping and feeds
    • Use of cool-mist humidifier and antipyretic
    • Bulb suctioning of oral and nasal secretions
    • Maintain hydration and feeding
    • Follow-up if patient worsens
  • Severe (< 28 days old, apnea, respiratory distress, lethargic):
    • Admit for inpatient care
    • Humidified oxygen and nebulized hypertonic saline
    • Suctioning of secretions
    • IV hydration
    • No evidence to support use of albuterol, epinephrine, or corticosteroids
  • Complications, such as pneumonia and respiratory failure, can occur and must be managed accordingly.

Prevention and Prognosis


  • Encourage breastfeeding.
  • Stop exposure to second-hand smoke.
  • Hand hygiene 
  • Palivizumab (monoclonal antibody) in high-risk patients: 
    • Meeting American Academy of Pediatrics (AAP) criteria for neonatal chronic lung disease:
      • Born at < 32 weeks gestation 
      • Requiring supplemental oxygen during the first 28 days of life
    • > 1 year old at onset of RSV season OR >2 years old but requiring medication for neonatal chronic lung disease


  • Bronchiolitis is self-limiting, lasting 7–10 days.
  • Only 3% of patients require hospitalization, and recover completely within 28 days.

Differential Diagnosis

  • Asthma: an inflammatory airway disease that leads to bronchial luminal narrowing and thus obstruction of airflow. Characterized by cough, wheezes, and dyspnea. Asthma is usually diagnosed after the age of 2 and has known triggers, with reversibility of symptoms with bronchodilator use in all cases, differentiating this condition from bronchiolitis.
  • Pneumonia: infection of the lower respiratory tract that results in symptoms very similar to bronchiolitis in infants. Patients with bronchiolitis may develop atypical pneumonia due to superimposed bacterial infections or worsened viral infections. Chest X-ray findings typically lag behind presentation in these cases, so the diagnosis is made when a patient has sustained hypoxia with increased oxygen supplementation, consolidations on lung exam, and increased work of breathing.
  • Gastroesophageal reflux disease (GERD): Acid reflux into the esophagus in infancy and childhood may present with intermittent cough and wheezing. May also be accompanied by a lack of weight gain and increased irritability. Gastroesophageal reflux disease can be differentiated from bronchiolitis if symptoms correlate to feeding routine and not seasonality. Bronchiolitis usually presents with a history of upper respiratory symptoms prior to wheezing.


  1. Teshome, Getachew, M.D., M.P.H., Gattu, R., M.D., & Brown, R., M.D. (2013). Acute bronchiolitis. Pediatric Clinics of North America, 60(5), 1019-1034. doi://
  2. Kliegman, R. M. et al. (2020). Wheezing, bronchiolitis, and bronchitis. In R. M. Kliegman MD et al., Nelson textbook of pediatrics (pp. 221–2221.e1).!/content/3-s2.0-B9780323529501004181
  3. Justice NA, Le JK. Bronchiolitis. (2020). Treasure Island (FL): StatPearls Publishing.

Study on the Go

Lecturio Medical complements your studies with evidence-based learning strategies, video lectures, quiz questions, and more – all combined in one easy-to-use resource.

Learn even more with Lecturio:

Complement your med school studies with Lecturio’s all-in-one study companion, delivered with evidence-based learning strategies.

🍪 Lecturio is using cookies to improve your user experience. By continuing use of our service you agree upon our Data Privacy Statement.