Is Bronchiolitis Only in Children Under Two?
No, bronchiolitis is not exclusively limited to children under two years of age, but it is overwhelmingly a disease of this age group and clinical practice guidelines specifically target children aged 1 month through 23 months for standardized management. 1
Age Distribution and Clinical Definition
The American Academy of Pediatrics (AAP) clinical practice guidelines specifically define the target population for bronchiolitis management as children from 1 month through 23 months of age. 1
Bronchiolitis is defined as a viral lower respiratory tract infection characterized by acute inflammation, edema, and necrosis of epithelial cells lining small airways, increased mucus production, and bronchospasm in infants and young children. 2, 3
Approximately 90% of children are infected with RSV (the most common cause) within the first 2 years of life, with up to 40% developing lower respiratory tract infection. 2, 1
The disease is most common in infants less than 1 year old, who account for the majority of hospitalizations (more than 90,000 annually in the United States). 1, 4
Why the Two-Year Cutoff Exists
The two-year age cutoff is used clinically because bronchiolitis represents the first episode of viral-induced wheezing in young children whose small airways are particularly susceptible to obstruction. 3
After the first year of life, children with recurrent wheezing episodes are more likely to have asthma rather than bronchiolitis. 4
The clinical presentation, pathophysiology, and management considerations differ significantly between infants under 2 years and older children, justifying the age-based distinction. 1
Important Clinical Caveats
Children outside the 1-24 month age range may develop bronchiolitis-like illnesses but may have different clinical presentations, management needs, and outcomes. 1
Neonates under 1 month with bronchiolitis symptoms require special consideration due to higher risk of severe disease and apnea. 1
Infants younger than 12 weeks are at particularly high risk for severe disease and warrant closer monitoring. 2, 4
The diagnosis cannot simply be made using a certain cutoff age alone—viral etiology and clinical presentation are critical differentiating factors. 5
Age-Specific Clinical Presentations
In infants 1-12 months: Bronchiolitis more likely presents with increased work of breathing including tachypnea, nasal flaring, intercostal retractions, and higher risk of apnea (particularly in those younger than 1 month and premature infants). 1
In children 12-24 months: Bronchiolitis typically presents with rhinitis and cough progressing to wheezing and rales, with better ability to compensate for increased respiratory effort compared to younger infants. 1
Practical Implications
The AAP guidelines exclude children with immunodeficiencies, underlying respiratory illnesses, neuromuscular disease, or hemodynamically significant congenital heart disease from general management recommendations, as these patients require individualized approaches regardless of age. 1, 4
Children with persistent respiratory symptoms beyond 4 weeks may represent a different clinical problem termed "post-bronchiolitis syndrome" rather than acute bronchiolitis. 1, 3
The mean time to cough resolution is 8-15 days, with 90% of children cough-free by day 21. 3