579 - Bronchiolitis after Introduction of RSV Vaccines: Shifting Patterns in Pediatric Hospitalizations

Publication Number: 2564.579

Carlos A. Gonzalez, Creighton University School of Medicine, Phoenix, AZ, United States; Nirmala P. Narla, Phoenix Children's Hospital, Phoenix, AZ, United States; Richard Engel, Phoenix Children's Hospital, Phoenix, AZ, United States; Jared Kusma, Phoenix Children's, Phoenix, AZ, United States

Background: Bronchiolitis is the leading cause of hospitalization in infants under one year, with Respiratory Syncytial Virus (RSV) as the primary pathogen. Pandemic public health measures sharply reduced bronchiolitis cases, followed by atypical interseasonal RSV surges that disrupted prior seasonal patterns. Continued monitoring is essential, particularly with the introduction of new RSV immunoprophylaxis and rising vaccine hesitancy.

Objective: Describe trends in bronchiolitis emergency department presentations and hospitalization rates across 2018-2025 bronchiolitis seasons.

Design/Methods: We conducted an IRB-approved retrospective cohort study of patients ≤24 months presenting with bronchiolitis at a tertiary children's hospital from October 2018-April 2025 (bronchiolitis season: Oct 1-Apr 30). Cases were identified using ICD-10 codes from ED and inpatient encounters. Seasons 2020-2021 and 2021-2022 were excluded due to pandemic-related viral disruption. Exclusions included asthma, congenital heart disease, home oxygen, and direct admissions. Chi-square tests compared presentation and admission rates; admissions were stratified by floor vs ICU. Wilson intervals calculated 95% CIs. Sub-analyses included RSV-positive bronchiolitis (RPB) and age groups (0-7 vs 8-24 months). Bonferroni significance: p< 0.005.

Results: We identified 12,741 patients, including 3,493 RPB cases. Bronchiolitis visits increased to 6.2% (6.0%-6.4%) of ED encounters in 2024-2025 vs 4.0% (3.9%-4.2%) from 2018-2023. RPB visits rose from 0.85% (0.78%-0.93%) in 2018-2019 to 2.45% (2.3%-2.6%) in 2024-2025. Despite increased presentations, hospitalization rates declined from 36.1% (34%-38%) in 2022-2023 to 18.2% (17%-20%) in 2024-2025. ICU admission among hospitalized patients remained stable (4.3% to 3.8%). Age-stratified trends were similar. Among RPB patients, admissions declined from 30% (28%-32%) in 2018-2019 to 18.2% (17%-20%) in 2024-2025, including decreases in floor (56.8% to 14.9%) and ICU admissions (8.3% to 3.5%). RSV testing increased from 35.8% to 59.3%.

Conclusion(s): These findings add to growing evidence of shifting pediatric respiratory patterns after the COVID-19 pandemic and represent one of the first analyses to include 2024-2025 data following the introduction of new RSV immunoprophylaxis. These findings support the need for ongoing surveillance and flexible resource planning. Future studies should incorporate individual vaccination status and assess social and viral co-factors driving evolving bronchiolitis patterns.

TABLE 1. Admission Rate for Bronchiolitis by RSV Season
Superscripts denote seasons that are significantly different from each other based on pairwise chi-square tests (p < 0.005). Seasons that do not share a superscript letter are significantly different. Confidence intervals calculated via Wilson Score Interval. ICU: Intensive Care Unit, RSV: Respiratory Syncytial Virus, CI: Confidence Interval

TABLE 2. Admission Rate for RSV-Positive Bronchiolitis by RSV Season
Superscripts denote seasons that are significantly different from each other based on pairwise chi-square tests (p < 0.005). Seasons that do not share a superscript letter are significantly different. Confidence intervals calculated via Wilson Score Interval. ICU: Intensive Care Unit, RSV: Respiratory Syncytial Virus, CI: Confidence Interval

TABLE 3. Age-Stratified Analysis of Total Admission and Presentation Rates for Bronchiolitis and RSV-Positive Bronchiolitis Patients by RSV Season
Superscripts denote seasons that are significantly different from each other based on pairwise chi-square tests (p < 0.005). Seasons that do not share a superscript letter are significantly different. Confidence intervals calculated via Wilson Score Interval.