Factors associated with mild bronchiolitis in young infants.

Objective: Bronchiolitis within the first 3 months of life is a risk factor for more severe illness. We aimed to identify characteristics associated with mild bronchiolitis in infants ≤90 days old presenting to the emergency department (ED). Methods: We conducted a secondary analysis of infants ≤90 days old with clinically diagnosed bronchiolitis using data from the 25th Multicenter Airway Research Collaboration prospective cohort study. We excluded infants with direct intensive care unit admissions. Mild bronchiolitis was defined as (1) sent home after the index ED visit and did not have a return ED visit or had a return ED visit without hospitalization, or (2) were hospitalized from the index ED visit to the inpatient floor for <24 hours. Multivariable logistic regression, adjusting for potential clustering by hospital site, was used to identify factors associated with mild bronchiolitis. Results: Of 373 infants aged ≤90 days, 333 were eligible for analysis. Of these, 155 (47%) infants had mild bronchiolitis, and none required mechanical ventilation. Adjusting for infant characteristics, clinical factors associated with mild bronchiolitis included older age (61-90 days vs 0-60 days) (odds ratio [OR] 2.72, 95% confidence interval [CI] 1.52-4.87), adequate oral intake (OR 4.48, 95% CI 2.08-9.66), and lowest ED oxygen saturation ≥94% (OR 3.12, 95% CI 1.55-6.30). Conclusions: Among infants aged ≤90 days presenting to the ED with bronchiolitis, about half had mild bronchiolitis. Mild illness was associated with older age (61-90 days), adequate oral intake, and oxygen saturation ≥94%. These predictors may help in the development of strategies to limit unnecessary hospitalization in young infants with bronchiolitis.