Epidemiological trends and seasonality of respiratory syncytial virus infection in children based on sentinel hospital surveillance data

Respiratory syncytial virus (RSV) represents the leading cause of acute lower respiratory tract infections and hospitalization among young children globally. Understanding the epidemiological trends and seasonal patterns of RSV infection is essential for developing effective prevention strategies and optimizing healthcare resource allocation. This retrospective study aimed to characterize the epidemiological trends, seasonal patterns, and risk factors associated with RSV infection in children younger than five years using sentinel hospital surveillance data spanning January 2018 to December 2023. A retrospective analysis was conducted using data from Yancheng No.1 People’s Hospital, the pediatric sentinel site of the Regional Respiratory Pathogen Surveillance System serving an urban and peri-urban catchment of approximately 1.8 million residents. Children under five years presenting with acute respiratory tract infections were enrolled when they had at least one major respiratory symptom and illness duration of 7 days or less, and nasopharyngeal specimens were tested for RSV by real-time reverse transcription polymerase chain reaction (RT-PCR). Demographic characteristics, clinical presentations, disease severity, seasonal distribution, and age-stratified severity patterns were analyzed. Multivariable logistic regression and sensitivity analyses clustered by patient identifier were used to identify factors associated with RSV positivity. Among 42,856 children tested, 7634 (17.8%) were RSV-positive. The highest detection rate occurred in children aged 6–11 months (24.3%), followed by those under 6 months (21.7%). Males demonstrated higher positivity than females (19.2% vs. 16.1%, P < 0.001), although the underlying cohort sex structure remained close to the municipal under-5 population distribution. Before the COVID-19 pandemic, RSV activity generally began in October and peaked in November–December; circulation was almost absent in 2020, shifted to an out-of-season summer peak in 2021, and rebounded sharply in late 2022. Children aged under 12 months (adjusted OR = 2.34, 95% CI 2.08–2.63), male sex (adjusted OR = 1.24, 95% CI 1.15–1.34), and absence of breastfeeding (adjusted OR = 1.43, 95% CI 1.28–1.60) were independently associated with RSV positivity. ICU admission increased from 4.2% before the pandemic to 6.8% in 2022–2023, and the association between the 2022–2023 surge and severe or critical disease persisted after age adjustment (adjusted OR = 1.29, 95% CI 1.11–1.50). RSV infection in young children showed marked age-dependent susceptibility and clear seasonal regularity that was substantially altered during the COVID-19 pandemic. The post-pandemic resurgence was associated with greater clinical severity and a modest shift toward older hospitalized children, supporting continued sentinel surveillance and timely deployment of RSV prevention strategies for infants and other vulnerable pediatric groups.