Bronchiolitis Post Introduction of RSV Immunoprophylaxis: Shifting Patterns in Pediatric Hospitalizations.

Bronchiolitis is the leading cause of hospitalization in infants under 12 months of age, most often due to respiratory syncytial virus (RSV). Following pandemic-related seasonal disruptions and the introduction of RSV immunoprophylaxis, monitoring bronchiolitis trends is essential for public health planning and resource allocation. We conducted an institutional review board approved retrospective cohort study of children aged ≤ 24 months who presented to a tertiary children's hospital with bronchiolitis during RSV seasons (October-April) from 2018-2019 through 2024-2025, excluding 2020-2022 due to COVID-19-related disruptions. Among 12 741 included patients, 3493 had RSV-positive bronchiolitis. In the 2024-2025 season, bronchiolitis accounted for 6.2% (6.0%-6.4%) of emergency department (ED) visits, up from approximately 4% in the 2018-2023 seasons (Table 1). Despite increased ED presentations, the proportion of bronchiolitis patients requiring hospitalization declined, while intensive care unit (ICU) admission rates remained stable. Respiratory syncytial virus testing among bronchiolitis patients increased from 35.8% (34.0%-38.0%) in 2018-2019 to 59.3% (57.0%-61.0%) in 2024-2025. Trends were consistent in age-stratified and RSV-positive subgroups. Findings highlight a meaningful shift in bronchiolitis epidemiology, underscoring the need for ongoing surveillance and adaptable clinical planning.