Bronchiolitis is the most common lower respiratory tract infection in patients under two years of age and the leading cause of hospital admission for those under six months of age .¹ This past winter saw a huge rise in pediatric respiratory illness in North America as well as an increased admission rate for children with bronchiolitis.² There is a wide spectrum of severity of illness as well as a huge variation in practice in treating these children.³ Complicating the approach to bronchiolitis further, the definition of bronchiolitis varies across guidelines, and while about 60 percent of bronchiolitis is caused by respiratory syncytial virus, 20 percent is caused by rhinovirus, which confers a 59 percent risk of developing asthma.⁴ While most children with bronchiolitis can be diagnosed without any workup and will improve with simple interventions and be discharged home, we need to know when to worry about the few who will require complex care, and this is sometimes challenging to sort out.

The Clinical Diagnosis

Bronchiolitis is a clinical diagnosis based on patient age, time of year, and clinical presentation. The typical patient with bronchiolitis is a child under 12 months of age who, during fall and winter months in northern climates, has a two- to three-day upper-respiratory-tract-infection prodrome and then develops symptoms of a lower respiratory tract infection with increased work of breathing, crackles, and wheezes, as well as poor feeding.⁵ It is important for clinicians and families to understand that acute symptoms usually last for approximately 10 days, but that the cough can last up to three weeks. Neonates may present with apnea and/or cyanosis.⁶

During the initial ED assessment, it can sometimes be difficult or even impossible to distinguish bronchiolitis from upper respiratory infection with asthma and bronchiolitis from bacterial pneumonia, as their clinical presentations overlap.⁷ Clinical presentations that suggest an alternative diagnosis to bronchiolitis include prolonged wheeze (three weeks or more), failure to thrive, recurrent feeding issues, choking with feeds, previous bacterial pneumonia, and the critically ill patient.⁵ Multiple wheezing episodes at any age increases the likelihood of asthma.⁴ The diagnosis of asthma can be tentatively made in otherwise healthy children as early as 12 months of age, using the following criteria: two or more episodes of wheezing, emergency department (ED) presentation of wheeze needing treatment, reversibility of respiratory distress after therapy, or first-time wheeze with response to therapy.⁸ The early diagnosis of asthma is important because literature suggests that a subset of patients with bronchiolitis develop abnormal lung function by the age of five years and long-term lung disease, and that this may be prevented with three-month courses of corticosteroids following each acute exacerbation.⁹ Bacterial pneumonia, which can occur concurrently with bronchiolitis, can be distinguished from bronchiolitis by the following clinical findings: high fever, toxic appearance, absence of wheeze, and unilateral chest findings.¹⁰