Infectious Disease · Bronchiolitis
The facts most likely to be tested
Press 1–5 to rate · ↑↓ to navigate
Respiratory syncytial virus is the most common cause of bronchiolitis in infants younger than 12 months.
Clinical presentation typically begins with upper respiratory tract symptoms followed by lower respiratory tract involvement including wheezing, tachypnea, and respiratory distress.
Diagnosis of bronchiolitis is clinical, based on history and physical examination, and does not require routine viral testing or chest radiography.
Management of bronchiolitis is primarily supportive, focusing on nasal suctioning and maintaining adequate hydration.
Nirsevimab (a long-acting monoclonal antibody) is now recommended for ALL infants <8 months entering their first RSV season; palivizumab is reserved for select high-risk infants and is being phased out (unavailable after Dec 31, 2025).
The most common complication of RSV infection in infants is acute respiratory failure or apnea, particularly in those born prematurely.
RSV is a paramyxovirus that causes syncytia formation in infected cells, leading to airway obstruction via mucus plugging and edema.
Vignette unlocked
A 4-month-old male is brought to the emergency department by his mother due to 3 days of nasal congestion, cough, and decreased oral intake. On physical examination, the infant is tachypneic with a respiratory rate of 62 breaths/min and has intercostal retractions. Lung auscultation reveals diffuse expiratory wheezing and crackles. The infant is afebrile, and oxygen saturation is 93% on room air.
What is the most appropriate management for this patient?
Supportive care with nasal suctioning and hydration
The patient presents with classic signs of bronchiolitis, which is a clinical diagnosis requiring supportive care rather than antibiotics or bronchodilators.
Full handout
High yield triage
Etiology / Epidemiology
Most common cause of bronchiolitis in infants < 2 years. Peak incidence in winter months.
Clinical Manifestations
Starts as URI, progresses to wheezing, respiratory distress, and nasal flaring.
Diagnosis
Nasopharyngeal swab PCR is the gold standard. Diagnosis is primarily clinical.
Treatment
Supportive care (nasal suctioning, hydration). No role for systemic steroids or antibiotics.
Prognosis
Most recover in 7-10 days. Apnea is a critical risk in premature infants.
Full handout
Epidemiology & Etiology
RSV was reclassified in 2016 into the family Pneumoviridae (genus Orthopneumovirus); previously grouped with Paramyxoviridae. It is the leading cause of hospitalization in infants. High-risk groups include prematurity, chronic lung disease, and congenital heart disease.
Pertinent Anatomy
Infection targets the lower respiratory tract, specifically the small-diameter bronchioles. The narrow airway caliber in infants makes them uniquely susceptible to obstruction from edema and mucus.
Pathophysiology
Viral invasion leads to epithelial necrosis and mucus plugging. This causes air trapping and atelectasis. The resulting inflammatory response triggers bronchospasm and increased airway resistance.
Clinical Manifestations
Initial symptoms include rhinorrhea and cough. Progression to bronchiolitis manifests as tachypnea, expiratory wheezing, and intercostal retractions. Cyanosis or apnea are red-flag signs requiring immediate ICU admission.
Diagnosis
Diagnosis is clinical based on age and respiratory findings. Nasopharyngeal swab PCR is the most sensitive test but is rarely required for routine cases. Chest X-ray is not indicated unless focal consolidation suggests secondary bacterial pneumonia.
Treatment
Management is supportive care including humidified oxygen and nasal suctioning. Systemic corticosteroids and bronchodilators are not recommended. Palivizumab is reserved for prophylaxis in high-risk infants during peak season.
Prognosis
Most patients recover fully. Apnea is a significant complication in infants < 6 weeks. Long-term follow-up may show increased risk of recurrent wheezing or asthma-like symptoms.
Differential Diagnosis
Asthma: usually > 2 years old with history of atopy
Foreign body aspiration: sudden onset, unilateral wheezing
Pneumonia: high fever, focal crackles on auscultation
Pertussis: classic whooping cough, post-tussive emesis
Cystic fibrosis: chronic failure to thrive, recurrent infections