What are the primary differential diagnoses for a patient presenting with bronchiolitis?

Differential Diagnoses for Bronchiolitis

When evaluating a child presenting with symptoms suggestive of bronchiolitis, clinicians must distinguish this viral lower respiratory tract infection from bacterial pneumonia, acute otitis media, asthma/reactive airway disease, congenital heart disease, and other serious bacterial infections—particularly urinary tract infections in young febrile infants.

Primary Differential Considerations

Bacterial Pneumonia

• Bacterial pneumonia with consolidation is the most critical differential to exclude, as it requires antibacterial therapy while bronchiolitis does not 1.
• Approximately 25% of hospitalized infants with bronchiolitis will have radiographic evidence of atelectasis or infiltrates that are often misinterpreted as possible bacterial infection 1.
• Bacterial pneumonia in infants with bronchiolitis without consolidation is unusual 1.
• The American Academy of Pediatrics emphasizes that routine chest radiography is not recommended for diagnosis of bronchiolitis, as it does not change management and may lead to unnecessary antibiotic use 1.

Serious Bacterial Infections (SBI)

• Urinary tract infections are the most common serious bacterial infection in infants with bronchiolitis, not bacteremia or meningitis 1.
• Multiple studies identified low rates of SBI (0%–3.7%) in patients with bronchiolitis and/or RSV infections 1.
• In one large study of 2,396 infants with RSV bronchiolitis, 69% of the 39 patients with SBI had a UTI 1.
• For febrile infants less than 28 days of age with bronchiolitis, the overall risk of SBI remains significant (approximately 10%), though not different between RSV-positive and RSV-negative groups 1.
• All SBIs in children between 29 and 60 days of age with RSV-positive bronchiolitis were UTIs, with a rate of 5.5% 1.

Acute Otitis Media (AOM)

• AOM is extremely common in bronchiolitic infants, occurring in 50-62% of cases 1.
• Although RSV alone can cause AOM, there are no clinical features that permit viral AOM to be differentiated from bacterial AOM 1.
• Bacterial pathogens (Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis) were isolated from 94% of middle-ear aspirates in one study 1.
• An additional 12% of patients developed AOM within 10 days of initial presentation 1.
• When AOM is identified, it should be managed according to AAP/AAFP guidelines for AOM diagnosis and management 1.

Asthma/Reactive Airway Disease

• Distinguishing first-time wheezing from recurrent wheezing is essential, as the underlying pathophysiology differs 2.
• Rhinovirus-induced wheezing is associated with atopic predisposition and high risk of subsequent asthma development, which may respond to systemic corticosteroids in severe illness 2.
• RSV-induced bronchiolitis is characterized by mechanical obstruction from mucus and cell debris rather than bronchospasm, explaining poor response to bronchodilators 2.
• Children with underlying chronic lung disease or recurrent wheezing are excluded from standard bronchiolitis management guidelines 1.

Congenital Heart Disease

• Infants with hemodynamically significant congenital heart disease present with similar respiratory symptoms but require different management approaches 1.
• These patients are at higher risk for severe disease and require close monitoring during oxygen weaning 1.

Other Viral Etiologies (Not True Differentials)

While these cause the same clinical syndrome of bronchiolitis, recognizing the specific viral etiology may have implications:

• Human metapneumovirus causes clinically indistinguishable bronchiolitis 1, 3.
• Influenza virus can cause bronchiolitis 1, 3.
• Adenovirus is a recognized cause 1, 3.
• Parainfluenza viruses cause bronchiolitis 1, 3.
• Human bocavirus is frequently detected in co-infection with RSV (88% of bocavirus-positive samples also had RSV) 4.
• Co-infection with RSV and bocavirus may require hospitalization more often (80% vs 60%) compared to RSV alone 4.

Clinical Approach to Differentiation

The diagnosis of bronchiolitis should be made on clinical grounds based on history and physical examination alone 1.

Key Clinical Features Supporting Bronchiolitis Diagnosis:

• Initial rhinitis and cough progressing to tachypnea, wheezing, rales, use of accessory muscles, and/or nasal flaring 1, 5.
• Age between 1 month and 23 months 1.
• Seasonal pattern (December through March in North America for RSV) 1, 3.

Red Flags Suggesting Alternative Diagnoses:

• Focal consolidation on examination suggests bacterial pneumonia rather than the diffuse findings of bronchiolitis 1.
• Fever in infants less than 28 days old warrants evaluation for SBI regardless of bronchiolitis diagnosis 1.
• Persistent fever or clinical deterioration should prompt consideration of bacterial co-infection 1.

Common Pitfalls to Avoid

• Do not routinely order chest radiographs, as atelectasis and infiltrates are common in bronchiolitis and lead to unnecessary antibiotic use 1.
• Do not assume all wheezing in infants is bronchiolitis—consider rhinovirus-induced wheezing in atopic children who may benefit from corticosteroids 2.
• Do not overlook UTI as the most likely SBI in young febrile infants with bronchiolitis, particularly those under 60 days of age 1.
• Antibacterial medications should be used only when specific indications of bacterial co-infection exist 1.