Acute Respiratory Tract Infections and Severe Disease Among Hospitalized Children.

Importance: The epidemiology of viral respiratory tract infections (RTIs) in children is constantly changing on the basis of transmission, seasonality, immunity, and disruptive events, such as pandemics. Objective: To describe the clinical characteristics and outcomes of children hospitalized with acute RTIs and to examine factors associated with risk of severe disease. Design, Setting, and Participants: This multisite, retrospective cohort study was conducted at 2 Canadian children's hospitals. Participants included children aged 0 to 18 years who were hospitalized with acute RTIs from July 1, 2022, to June 30, 2023. Follow-up for readmission was performed at 30 days after discharge. Analysis was conducted in June to November 2025. Exposure: Clinical and demographic factors, signs and symptoms, diagnostic testing, viral testing, management, and interventions. Main Outcomes and Measures: The primary outcome was the proportion of patients who developed severe disease, defined as the need for noninvasive or invasive mechanical ventilation, extracorporeal membrane oxygenation therapy, or kidney replacement therapy; cardiac arrest; or death. Demographics and clinical characteristics were also described. Multivariable robust Poisson regression was used to evaluate factors associated with risk of severe outcomes and was reported as adjusted risk ratios (aRRs) with 95% CIs. Results: There were 2585 children hospitalized with acute RTIs, with a median (IQR) age of 2.5 (0.9-5.0) years. There were 1542 male children (59.7%), and 1307 patients (50.6%) had at least 1 chronic condition, with neurologic, developmental, or genetic conditions being the most common. More than one-third (879 children [34.0%]) were transferred from a referring institution. Viral testing was performed for 2332 patients (90.2%), with a viral pathogen identified in 1828 (70.7%) of those tested. Viral coinfections were detected in 338 children. The most common viruses were respiratory syncytial virus (709 children) and enterovirus-rhinovirus (598 children). The median (IQR) length of hospital stay was 3 (2-6) days. Nearly one-quarter of children (551 children [21.3%]) developed severe disease. Those with 2 or more comorbidities (aRR, 1.62; 95% CI, 1.36-1.93) or who were transferred from a referring hospital (aRR, 4.73; 95% CI, 4.01-5.59) were at increased risk of severe disease. Conclusions and Relevance: This cohort study found that hospitalized children with acute RTIs frequently have underlying chronic conditions and often require intensive intervention. Understanding the epidemiologic profile and factors associated with risk of severe disease in this population can inform resource allocation to optimize outcomes for pediatric patients.