What are the key clinical features to differentiate bronchiolitis from other respiratory infections in infants?

Key clinical features that differentiate bronchiolitis from other respiratory infections in infants include:

• Age: Bronchiolitis primarily affects babies and children under 2 years, most commonly in the first year of life, peaking between 3 and 6 months.
• Prodrome: A coryzal (cold-like) prodrome lasting 1 to 3 days precedes the illness.
• Symptoms: Persistent cough combined with either tachypnoea (rapid breathing) or chest recession (or both).
• Auscultation findings: Presence of wheeze and/or crackles on chest auscultation.
• Fever: Fever occurs in about 30% of cases, usually less than 39°C.
• Poor feeding: Typically develops after 3 to 5 days of illness.
• Apnoea: Young infants, especially under 6 weeks, may present with apnoea without other clinical signs.
• Oxygen saturation: Measurement is important; low saturation supports bronchiolitis diagnosis and severity assessment.
• Distinguishing from pneumonia: Pneumonia is more likely if there is a high fever (>39°C) and/or persistently focal crackles.
• Distinguishing from viral-induced wheeze or early asthma: Consider if there is persistent wheeze without crackles, recurrent episodic wheeze, or a personal/family history of atopy; these are unusual under 1 year.

These features help differentiate bronchiolitis from other respiratory infections such as pneumonia or viral-induced wheeze in infants ¹.