P-1204. Hospitalizations Associated with Respiratory Syncytial Virus (RSV) Illness Among Children and Adolescents in Ontario, Canada

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Abstract Background Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract illness (LRTI) among children, particularly in young infants. Although the burden of illness is higher at a younger age, it has been less documented in children 5-17 years old. *Missing and Not Applicable categories not considered while calculating % #Risk status includes conditions such as congenital malformations, cystic fibrosis, chronic respiratory disease, trisomy 21, cardiovascular disorders, congenital kidney disease (in < 2 years only), congenital neurological disorders (in < 2 years only), cancer (in 2-17 years only), immunodeficiencies (in 2-17 years only), and neuromuscular diseases (in 2-17 years only) RSV: respiratory syncytial virus; wGA: weeks of gestational age Methods Patients aged ≤ 17 years hospitalized with RSV between July 1st, 2010 and March 31st, 2023 were identified from provincial administrative data at ICES, which captures all healthcare encounters within Ontario’s publicly funded healthcare system. Annual outcomes were reported from July 1st to June 30th of the next year.Figure 1.RSV hospitalizations among Ontario children < 12 months old (2010 – 2023).Note that the age groups are not consistent in size (i.e., 1-month groups for those < 7 months while 7 - < 12 months were all grouped together). Results Overall, 23,930 RSV hospitalizations were reported; annual counts ranged between 1,356 (2010-11) and 4,298 (2022-23) (Table 1). Children < 12 months accounted for 66% of all hospitalizations, of which > 75% occurred in those < 6 months (Figure 1), and over 90% of hospitalizations occurred during the RSV-season (November-April). Although children < 2 years made up a greater proportion of hospitalizations compared to those 2-17 years (84% vs. 16%), risk conditions were more common in those 2-17 years compared to < 2 years of age (35% vs. 7%). The median length of stay (LOS) per RSV hospitalization was 69 hours (h). Longer LOS was observed for those hospitalized at age < 1 month (108 h), 5-17 years (92 h), born preterm (84-115 h), with a low birthweight (87-119 h), or with a risk condition (92-97 h). About 12% of the cohort had an intensive care unit (ICU) stay (median LOS: 87 h), which made up 55% of their LOS in the hospital. A greater proportion of those hospitalized at < 4 months old (16%) or 5-17 years old (22%) had an ICU stay. While the proportion of patients with an ICU stay increased from 8% in 2010-11 to 17% in 2022-23, the median LOS in ICU decreased from 101 h to 78 h over the same period. Overall, in-hospital, all-cause mortality was 0.12%, but higher for those with risk conditions (< 2 years: 0.61%; 2-17 years: 1.02%). Conclusion This study highlighted those who may be more impacted by RSV illness: younger infants, those born prematurely or with a low birthweight, and with underlying risk conditions. While most hospitalizations were observed in those < 12 months, RSV remains a noteworthy cause of hospitalization in older children, especially those with risk conditions. Disclosures Sazini Nzula, PhD, Pfizer Canada: Employee Alexandra Goyette, MSc, Pfizer: Employee|Pfizer: Stocks/Bonds (Private Company) Deshayne B. Fell, PhD, Pfizer Inc.: Employment|Pfizer Inc.: Stocks/Bonds (Private Company) Ana Gabriela Grajales, MD, Pfizer Canada ULC: I am currently an employee in Medical Affairs|Pfizer Canada ULC: Stocks/Bonds (Public Company)