Bronchiolitis
Pediatrics
Illness script · Pediatrics
Bronchiolitis
Viral lower respiratory tract infection causing small airway inflammation and obstruction, predominantly in infants <2 years old.
This illness script for Bronchiolitis covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Most common in infants 2–6 months; peak incidence winter months
- RSV accounts for ~80% of cases; also hMPV, parainfluenza, rhinovirus
- Prematurity, chronic lung disease, congenital heart disease → severe disease
- Daycare attendance, siblings, smoke exposure increase risk
- Not vaccinated (palivizumab is prophylaxis, not vaccine)
02
Presentation
- Prodrome: 2–3 days of URI symptoms (rhinorrhea, low-grade fever)
- Progresses to cough, tachypnea, increased work of breathing
- Classic exam: diffuse wheezing + crackles in infant <2 years
- Nasal flaring, intercostal/subcostal retractions, grunting
- Hypoxia (SpO2 <90%) signals severity; apnea risk in neonates/ex-premies
- Chest hyperinflation on exam; feeding difficulty common
03
Pathophysiology
- Viral infection → bronchiolar epithelial necrosis and edema
- Mucus plugging + inflammatory debris → air trapping and atelectasis
- Increased airway resistance → wheezing, hyperinflation, V/Q mismatch
- Infants vulnerable due to small airway diameter and poor collateral ventilation
04
Diagnostics
- Diagnosis is CLINICAL — no routine labs or imaging required
- CXR if needed: hyperinflation, peribronchial thickening, patchy atelectasis (can mimic pneumonia)
- RSV rapid antigen test available but does not change management
- Pitfall: atelectasis on CXR often misread as pneumonia → avoid unnecessary antibiotics
- Pulse oximetry guides severity and admission decision
05
Management
- Supportive care is mainstay: nasal suctioning, hydration, supplemental O2
- O2 supplementation to maintain SpO2 ≥90–92%
- High-flow nasal cannula (HFNC) for moderate-severe respiratory distress
- Admit if SpO2 <90%, apnea, poor feeding, or severe retractions
- Bronchodilators (albuterol) NOT routinely recommended — no proven benefit
- Corticosteroids and antibiotics are NOT indicated
- Palivizumab (anti-RSV monoclonal Ab) for high-risk prophylaxis only
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Asthma (reactive airway disease)
Age >2 years, recurrent episodes, family/personal atopy history, responds to bronchodilators
Bacterial pneumonia
High fever, lobar consolidation on CXR, toxic appearance, productive cough — not typical URI prodrome
Croup (laryngotracheobronchitis)
Barky/seal-like cough, stridor (upper airway), no wheezing, older infant/toddler
Foreign body aspiration
Sudden onset without viral prodrome, unilateral wheeze, localized hyperinflation on CXR
Keep reading
Full library- Bacterial MeningitisAcute bacterial infection of the subarachnoid space causing meningeal inflammation, often rapidly fatal without treatment.
- CellulitisAcute bacterial infection of the deep dermis and subcutaneous fat, most often caused by Streptococcus pyogenes or Staphylococcus aureus.
Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.