344 - Severity of Illness in Bronchiolitis Amid Unusual Seasonal Pattern During the COVID-19 Pandemic

Poster Number: 344
Publication Number: 344.204

Kristen H. Shanahan, Boston Children's Hospital, Boston, MA, United States; Michael C. Monuteaux, Boston Children's Hospital, Boston, MA, United States; Richard Bachur, Boston Children's Hospital, Boston, MA, United States

Background: Bronchiolitis is primarily caused by respiratory syncytial virus (RSV), historically peaking in the winter. An epidemic of RSV did not occur in the winter of 2020-2021. Experts raised concerns about potentially low herd immunity leading to prolonged subsequent surges or more severe illness. Data is very limited on severity of illness in bronchiolitis in 2021.

Objective: Our objectives were to characterize recent trends in bronchiolitis and to compare severity of illness in bronchiolitis in the most recent year to prior seasonal epidemics.

Design/Methods: This cross-sectional study included United States (US) children’s hospitals in the Pediatric Health Information Systems database. We included children under 24 months old presenting to the emergency department (ED) with bronchiolitis from October 2016 to September 2021. To allow for winter epidemics to be captured continuously, years were defined from October of one year to September of the following year. We estimated simple logistic regression models with clinical outcomes (hospitalization, intensive care admission, invasive mechanical ventilation, or non-invasive ventilation) as the dependent variable and time period (October 2020 – September 2021 versus October 2016 – September 2020) as the independent variable. Secondary logistic regression models for the clinical outcomes were adjusted for age. We estimated Fourier Poisson regression models to test whether the pattern of seasonality for ED visits for bronchiolitis differed by time period. All models were adjusted for clustering by hospital.

Results: The study included 389,411 ED visits at 46 children’s hospitals (Table 1). Rates of hospitalization, intensive care admission, invasive mechanical ventilation, or non-invasive ventilation did not differ significantly between October 2020 – September 2021 compared to prior years (p < 0.001, Table 2). Seasonality in bronchiolitis differed significantly in October 2020 – September 2021 compared to prior years (p < 0.001, Table 1). A delayed peak in bronchiolitis occurred in August 2021 following an unusual seasonal pattern (Figure 1).Conclusion(s): This study of 46 US children’s hospitals characterizes unusual seasonality in bronchiolitis in 2021. However, severity of illness in infants with bronchiolitis from October 2020 – September 2021 was consistent with prior epidemics. As the implications of the unusual seasonality of bronchiolitis remain unknown, emerging trends in bronchiolitis warrant close attention.
Kristen Shanahan - Curriculum Vitae 12/2021Kristen Shanahan CV 12.14.2021.pdf
Table 2. Logistic Regression Models for Clinical Outcomes for Bronchiolitis at US Children’s Hospitals in October 2020 – September 2021 Compared to October 2016 – September 2020