RSV bronchiolitis is the most common lower respiratory tract infection in infants and the leading cause of infant hospitalization, with RSV accounting for 60–80% of bronchiolitis cases. [1-2] Diagnosis is clinical — routine laboratory testing, viral testing, and radiography are not recommended per AAP guidelines. [1][3] Treatment is primarily supportive; no pharmacologic therapy has been shown to shorten the disease course. [1][3-4]
1. History
- HPI essentials: Duration of URI prodrome (typically 2–4 days of rhinorrhea, congestion, sneezing, low-grade fever), followed by cough, increased work of breathing, and feeding difficulty [1-2]
- Timing: Incubation period 4–6 days; peak severity typically day 3–5 of illness; improvement over 7–14 days; 90% have cough resolution within 3 weeks [2]
- Feeding assessment: Quantify oral intake — decreased feeding is both a severity marker and a driver of dehydration (OR 1.9 for hospitalization) [1]
- Apnea history: Ask specifically about witnessed pauses in breathing, especially in neonates and young infants [1][5]
- Important negatives: Absence of URI prodrome should raise suspicion for non-infectious causes (cardiac disease, airway anomaly, foreign body) [2][6]
2. Alarm Features
- SpO₂ < 90% (OR 8.9 for need for respiratory support) [1]
- Nasal flaring / grunting (OR 3.8) [1]
- Apnea (OR 3.0) — especially in neonates and infants < 2 months [1][5]
- Retractions (intercostal, subcostal, supraclavicular) (OR 3.0) [1]
- Age ≤ 2 months (OR 2.1) [1]
- Dehydration / poor feeding (OR 2.1 / 1.9) [1]
- Cyanosis, lethargy, or irritability — indicators of impending respiratory failure [5]
- Neonates may present with a sepsis-like illness or isolated apnea without classic respiratory findings [5][7]
The following figure from a JAMA Network Open study illustrates how clinical signs differ by age and intubation status in infants requiring ICU care for RSV — notably, the youngest infants present more often with apnea rather than classic respiratory symptoms:
3. Medications
- Not recommended (per AAP/NICE): Bronchodilators, nebulized epinephrine (inpatient), corticosteroids, nebulized hypertonic saline, antibiotics, chest physiotherapy [1][3]
- Bronchodilators do not improve SpO₂, hospital admissions, length of stay, or duration of illness and cause adverse effects (tachycardia, tremor, desaturation) [1]
- Corticosteroids (systemic or inhaled) do not reduce admissions or length of stay [1]
- Antibiotics only if concurrent bacterial infection is documented; bacterial co-infection rate is < 11%, yet ~30% of children receive unnecessary antibiotics [5]
- Antipyretics (acetaminophen, ibuprofen per age) for comfort
- Nebulized epinephrine may reduce ED admissions if given within 24 hours of outpatient presentation (NNT = 5), but is not recommended for inpatients [1]
4. Diet
- Maintain hydration and nutrition — the primary non-respiratory concern
- If unable to maintain oral intake due to respiratory distress, use nasogastric (preferred) or IV isotonic fluids; two RCTs showed no difference in outcomes between NG and IV routes, but NG has fewer complications [5]
- Small, frequent feeds may be better tolerated than large-volume feeds
- Breastfeeding should be encouraged when possible; breastfeeding for < 2 months is a risk factor for severe disease [2]
5. Review of Systems
- Respiratory: Cough character, wheeze, stridor, breathing pauses, noisy breathing
- GI: Vomiting with cough, decreased wet diapers (dehydration marker), feeding refusal
- Neurologic: Lethargy, irritability, altered mental status (may indicate hypoxia or rare extrapulmonary complications such as encephalitis) [2]
- Cardiac: Tachycardia out of proportion to fever (consider myocarditis or arrhythmia) [8-9]
- Fever pattern: Fever is present in only ~15% of RSV cases; new or recurrent fever later in illness should raise concern for bacterial superinfection [5]
6. Collateral History and Family History
- Sick contacts: Daycare attendance, household members with URI symptoms
- Smoke exposure: Cigarette smoke exposure is an independent risk factor for severe disease [2][10]
- Family history of asthma/atopy: May predispose to both severe bronchiolitis and subsequent recurrent wheezing [2][11]
- Birth history: Gestational age, NICU stay, chronic lung disease, congenital heart disease
- Immunization/prophylaxis status: Nirsevimab or maternal RSV vaccination status [12-13]
7. Risk Factors
- Prematurity (especially < 29–32 weeks' gestation) [2][6]
- Age < 10–12 weeks at presentation [2]
- Chronic lung disease (bronchopulmonary dysplasia) [6]
- Hemodynamically significant congenital heart disease [6]
- Immunodeficiency or neuromuscular disease [6]
- Exposure to cigarette smoke [2][10]
- Breastfeeding < 2 months [2]
- Low socioeconomic status, crowded living conditions [2][14]
- Male sex [14]
- Down syndrome [14]
- Indigenous ethnicity (Australian Aboriginal, First Nations, Māori) [2][10]
- Risk factors are additive — multiple factors compound the likelihood of severe disease [2]
8. Differential Diagnosis
- Pertussis — paroxysmal cough, post-tussive emesis, apnea; consider if severe cough or known exposure [2][6]
- Bacterial pneumonia — new fever, focal consolidation, clinical deterioration outside typical bronchiolitis trajectory [2]
- Reactive airway disease / asthma — recurrent wheezing episodes, family history, response to bronchodilators (more relevant in children > 12 months) [15]
- Congenital heart disease — absence of URI prodrome, hepatomegaly, murmur, failure to thrive [2][6]
- Congenital airway anomaly (vascular ring, tracheomalacia) — persistent stridor, no viral prodrome [6]
- Foreign body aspiration — sudden onset, unilateral wheeze, no prodrome [2]
- Myocarditis — tachycardia disproportionate to fever, poor perfusion, hepatomegaly [8]
9. Past Medical History
- Prior episodes of wheezing or bronchiolitis (by definition, bronchiolitis refers to the first episode of wheezing in children < 2 years) [14][16]
- History of prematurity, NICU admission, intubation
- Chronic lung disease, congenital heart disease, immunodeficiency
- Prior RSV prophylaxis (palivizumab or nirsevimab) [13][17]
- Surgical history (especially cardiac surgery)
10. Physical Exam
- Vitals: Tachypnea (age-adjusted), tachycardia, fever (low-grade, present in ~15%), SpO₂
- General: Level of alertness, hydration status (mucous membranes, fontanelle, skin turgor, capillary refill)
- Respiratory: Nasal flaring, grunting, intercostal/subcostal/supraclavicular retractions, accessory muscle use, head bobbing in infants [1]
- Auscultation: Diffuse wheezing, coarse crackles, prolonged expiratory phase; young infants may have fine rales without wheeze [1-2]
- Concerning findings: Cyanosis, apnea, poor air entry/silent chest, altered mental status
- Minute-to-minute variability in exam findings is characteristic due to mucus plugging and clearing — a period of observation is often needed to confirm clinical trajectory [2]
11. Lab Studies
- Routine labs are NOT recommended per AAP guidelines [1][3]
- RSV testing (rapid antigen or PCR): Not routinely needed for clinical management but may help with cohorting, antibiotic stewardship, and epidemiologic tracking [5][18]
- Consider labs if: Concern for bacterial co-infection (CBC, CRP, blood culture), dehydration (BMP), or sepsis workup in neonates
- Troponin / BNP: Consider if cardiac involvement suspected (rare); BNP combined with pulmonary consolidation may predict cardiovascular events in severe RSV [9][19]
- Blood gas: Only in severe respiratory distress or impending respiratory failure
12. Imaging
- Chest X-ray is NOT routinely recommended — leads to unnecessary antibiotic use without changing management [1][3]
- When to image: Atypical course, suspected pneumonia (focal findings, new fever, clinical deterioration), concern for foreign body, air leak (pneumothorax), or cardiac disease
- Typical CXR findings (if obtained): Hyperinflation, peribronchial thickening, patchy atelectasis [20]
- Consolidation on CXR does not necessarily indicate bacterial infection and should not automatically prompt antibiotics [5]
13. Special Tests
- No validated severity scoring tool is universally accepted for bronchiolitis, though several exist (e.g., Wang, RDAI, mTAL) with modest predictive ability [1-2][5]
- Point-of-care RSV molecular testing — rapid, sensitivity/specificity non-inferior to PCR; useful for cohorting and antibiotic stewardship [5]
- Multiplex respiratory viral panels — may identify co-infections (rhinovirus, metapneumovirus, parainfluenza) but rarely change acute management
- Continuous pulse oximetry is no longer required per AAP; intermittent monitoring is acceptable in stable patients [21]
14. ECG
- Not routinely indicated in bronchiolitis
- RSV has been associated with sinoatrial blocks (76.5% of RSV-positive infants in one systematic Holter study vs. 2.9% of RSV-negative), though these were transient and resolved within ~4 weeks [9]
- Reported cardiac arrhythmias include ectopic atrial tachycardia, chaotic atrial tachycardia, atrial flutter, and rarely sinus arrest [8-9][22]
- Indications for ECG/cardiac monitoring: Tachycardia disproportionate to fever, bradycardia, apnea with hemodynamic instability, suspected myocarditis [9][22]
- In structurally normal hearts, RSV-associated arrhythmias are self-limited and do not require prolonged antiarrhythmic therapy [22]
15. Assessment
- Clinical diagnosis based on history and physical exam in a child < 24 months with first episode of wheezing preceded by viral URI prodrome [1][3]
- Severity stratification relies on clinical assessment: work of breathing, feeding ability, hydration status, SpO₂ [1]
- Peak severity occurs around day 3–5 of illness — patients presenting early may worsen before improving [2]
- Atypical presentations: Neonates may present with apnea or sepsis-like illness without prominent respiratory findings; older infants present with more classic wheeze [5][7]
- Complications to consider: Respiratory failure (5–6% of hospitalized children require ICU), bacterial superinfection, pneumothorax (rare, more common in older infants), and rare extrapulmonary manifestations (encephalitis, cardiomyopathy, hepatitis) [2][15][20]
16. Treatment Plan
Initial stabilization
- Gentle nasal suctioning (avoid deep/aggressive suctioning) [1]
- Supplemental O₂ to maintain SpO₂ > 90% (evidence-based threshold per AAP and WHO) [1][5]
- Position of comfort; minimal handling in moderate-severe cases [5]
Respiratory support escalation
- Low-flow nasal cannula → High-flow nasal cannula (HFNC) → CPAP → Intubation/mechanical ventilation [1-2][5]
- HFNC has migrated from ICU to ward/ED use with growing evidence base [2]
Hydration
- NG tube (preferred) or IV isotonic fluids[5]
What NOT to do
Prevention (for future seasons)
- Nirsevimab (Beyfortus): Single IM dose for all infants entering first RSV season; 50 mg if < 5 kg, 100 mg if ≥ 5 kg; ~80% reduction in RSV hospitalization, ~90% reduction in ICU admission [12-13][23-24]
- Clesrovimab (Enflonsia): Recently FDA-approved alternative mAb for first RSV season [23]
- Maternal RSV vaccine (Abrysvo): RSVpreF vaccine at 32–36 weeks' gestation; ~82% efficacy against severe RSV LRTI through 90 days [12][25]
- Palivizumab: Monthly IM dosing reserved for high-risk infants (prematurity < 29 weeks, BPD, hemodynamically significant CHD) if nirsevimab unavailable [17][21]
17. Disposition
Admission criteria
- SpO₂ < 90% [1][5]
- Significant respiratory distress (nasal flaring, grunting, retractions) [1]
- Apnea [1]
- Inability to maintain oral hydration [1]
- Age ≤ 2 months (lower threshold for admission) [1]
- Multiple risk factors present simultaneously [1]
- Unreliable follow-up or caregiver concern
ICU admission triggers
- Impending respiratory failure, need for HFNC > ward capability, CPAP, or intubation
- Recurrent or prolonged apnea
- Hemodynamic instability
Discharge criteria
- SpO₂ consistently > 90% on room air (including during sleep and feeding) [5]
- Adequate oral intake (≥ 50–75% of baseline)
- Stable or improving respiratory status
- Caregivers comfortable with home management and return precautions
- Observation period: Consider 11 hours for infants ≥ 3 months and up to 25 hours for infants < 3 months to detect delayed desaturation [26]
18. Follow Up / Return Precautions
- Routine scheduled follow-up may not be necessary for uncomplicated bronchiolitis — a randomized trial (BeneFIT) found that as-needed follow-up was non-inferior to scheduled visits and may reduce unnecessary medication prescriptions [27]
- Return precautions (counsel caregivers):
- Breathing pauses or apnea
- Worsening work of breathing (rib retractions, nasal flaring, grunting)
- Refusal to feed or significantly decreased wet diapers
- Cyanosis or dusky color
- Lethargy or difficulty arousing
- New or recurrent fever after initial improvement (concern for bacterial superinfection)
- Expected course: Symptoms peak day 3–5, gradual improvement over 1–2 weeks, cough may persist up to 3 weeks [2]
- Long-term consideration: RSV bronchiolitis is associated with a 2- to 4-fold increased risk of recurrent wheezing in early childhood (meta-analysis OR 3.84); whether this is causal or reflects shared predisposition remains debated. Approximately 17–60% of hospitalized children develop recurrent wheezing in subsequent years, though the association attenuates with age [2][6][11][28]
References
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