Epidemiological Profiles of Respiratory Syncytial Virus Infection Among Hospitalized Children in a Tropical Setting: A Large Laboratory-Based Surveillance Study From Hainan, China.

Respiratory syncytial virus (RSV) is a leading cause of acute respiratory infection in young children, yet subtype-specific and age-stratified epidemiological patterns remain incompletely characterised in tropical settings. To address this gap, we aimed to assess the age distribution and seasonal patterns of RSV infections in a large hospitalized paediatric population. We analysed surveillance data from 27,440 children tested for RSV. Age-specific positivity and subtype distributions were estimated. Seasonal dynamics were assessed using generalised linear mixed models to estimate annual amplitude, peak timing, and epidemic duration. Multivariable logistic regression examined independent associations of age, sex, and season with RSV infection. Our results showed that RSV infection was highly concentrated in early life, and positive rates peaked at 27.7% (95% CI: 25.4-30.2) among infants aged 2-3 months and declined with age. The mean age at infection was 2.0 years (2.2 for RSV-A; 1.7 for RSV-B). RSV-B predominated in early infancy, whereas RSV-A became dominant from 1 year onward (p < 0.001). Transmission was strongly seasonal, with 76.8% of infections occurring during the rainy season. In conclusion, the RSV burden was concentrated in infancy, with distinct subtype-specific age patterns and pronounced rainy-season seasonality, informing the timing and targeting of RSV preventive strategies.