Risk Factors for Severe Disease Among Children Hospitalized With Respiratory Syncytial Virus.

Importance: A resurgence of respiratory syncytial virus (RSV)-associated acute respiratory tract infection (ARI) was observed in 2022 and 2023 after the COVID-19 pandemic. Changes in the demographic characteristics, disease severity, and outcomes of patients were observed, which could impact the identification of risk groups for interventions aimed at reducing the severity of RSV disease. Objectives: To identify factors associated with severe clinical outcomes among children hospitalized with RSV-associated ARIs in 2022 and 2023. Design, Setting, and Participants: This observational cohort study, conducted at 2 large, Canadian, tertiary-level pediatric hospitals, comprised all 709 cases of RSV-associated ARI among children younger than 18 years who were admitted to the hospital or intensive care unit (ICU) from July 1, 2022, to June 30, 2023. Exposure: Diagnosis of RSV-associated ARI. Main Outcomes and Measures: The primary outcome of severe disease was defined as requiring noninvasive or invasive ventilation or death. Risk factors for severe disease and ICU admission (secondary outcome) were assessed using multivariable Poisson regression, and results were reported as adjusted risk ratios (ARRs) with 95% CIs, with age-stratified models (<2 years and ≥2 years). Results: A total of 709 cases (median age, 13.1 months [IQR, 2.0-36.6 months]; 442 boys [62.3%]) were admitted with RSV-associated ARI; 452 (63.8%) were younger than 2 years, and 257 (36.2%) were aged 2 years or older. Severe disease was documented for 204 cases (28.8%). Patients with severe disease were younger than those with nonsevere disease (median age, 2.6 months [IQR, 1.3-16.0 months] vs 18.6 months [IQR, 4.5-39.1 months]; P < .001). Pulmonary disease and use of home oxygen (ARR, 2.47 [95% CI, 1.30-4.68]) and neurologic, neuromuscular, and developmental conditions (ARR, 1.89 [95% CI, 1.03-3.49]) were associated with severe disease among children aged 2 years or older. Among children younger than 2 years, age younger than 3 months (ARR, 2.34 [95% CI, 1.43-3.84]), age 3 to less than 6 months (ARR, 2.79 [95% CI, 1.65-4.70]), and prematurity (ARR, 1.40 [95% CI, 1.03-1.89]) were associated with severe disease. Conclusions and Relevance: In this cohort study of children hospitalized with RSV in 2022 and 2023, severe RSV disease was more likely among those aged 2 years or older with pulmonary and neurologic, neuromuscular, or developmental conditions. For children younger than 2 years, age younger than 6 months and prematurity were the main risk factors. These findings support prevention strategies for all younger children, including premature infants, with potential benefit for children aged 2 years or older in specific high-risk groups.