Viral infection of the lower respiratory tract, usually from November to April

Usually in children < 2 years of age

Bronchiolitis, viral induced reactive airways disease, and the first episode of asthma are clinically indistinguishable

Children with atopy or family history of atopy or severe bronchiolitis requiring hospitalization have increased probability of developing asthma

Characterized by preceding coryza and cough, followed by respiratory distress

Respiratory distress is associated with tachypnea, chest retractions, and expiratory wheezing

Fever may or may not be present and crepitations are often heard

Severe bronchiolitis: may see grunting, nasal flaring, and poor air entry

Associated agitation, lethargy, pallor, cyanosis, apnea accompany impending respiratory failure

Wheezing may be absent, especially at initial presentation

Wheezing may appear after a trial of inhaled bronchodilators

Although persistent absence of wheezing should prompt consideration of other diagnoses, it does not rule out bronchiolitis

Wheezing in bronchiolitis is often a low-pitched, rhonchi-like quality

Antecedent coryza and worsening cough

Cough may be severe and at times paroxysmal and suggest pertussis

Occasional vomiting after cough is common

Bronchiolitis vs pertussis:

Decreased oral intake is common, even in mild bronchiolitis

Symptoms usually abate in 2-3 weeks, rarely last 3-4 weeks or longer

High-risk history that may be associated with more severe disease or need for hospitalization: age < 6-8 weeks, prematurity, neonatal ventilation, coexistent chronic lung disease, hemodynamically significant heart disease, neuromuscular disease, immunodeficiency

Nontoxic appearance (fever may be high)

Absence of agitation/pathologic lethargy

Normal level of consciousness for time of day

Dehydration is rare despite decreased oral intake

Degree of tachypnea is highly variable: persistent RR ≥80 is usually associated with severe disease

Suprasternal and supraclavicular retractions may be difficult to see due to the short neck