A Shift in the Respiratory Syncytial Virus Seasonal Pattern: A Single–Center Retrospective Study in Anhui, China (2023–2025)

Objective: Before the coronavirus disease 2019 pandemic, respiratory syncytial virus (RSV)-related hospitalizations followed a predictable seasonal pattern in Anhui, China, typically beginning in November and lasting until March of the following year. However, city-specific data for Anhui were limited. This study investigated the epidemiological patterns and risk factors associated with severe RSV-associated lower respiratory tract infection (LRTI) among hospitalized children in our centre. Methods: We reviewed the records of children aged ≤14 years who were hospitalized with RSV lower respiratory tract infection between June 2023 and May 2025. RSV infection was confirmed using reverse transcription-polymerase chain reaction testing. Data on demographics, clinical presentation, and laboratory findings were extracted from electronic medical records. We analyzed seasonal trends and used logistic regression to identify independent predictors of severe RSV infection. Results: Among 5,755 children tested for respiratory pathogens, 448 tested RSV-positive (overall positivity rate 7.79%). The positivity rate increased from 6.47% (194/3,000) in 2023–2024 to 9.22% (254/2,755) in 2024–2025. A marked epidemiological shift was observed: the 2024–2025 RSV seasonal outbreak began approximately one month earlier and persisted approximately one month longer than that of the prior season. After excluding ten patients with incomplete data, 438 children were included in the clinical analysis; of these, 82 (18.72%) had severe disease. Multivariable logistic regression analysis identified that age under 6 months, congenital heart disease, and preterm birth were each independent risk factors for severe RSV-associated LRTI. Conclusion: The overall RSV positivity rate among hospitalized children with respiratory symptoms was 7.79%, which increased from 6.47% in 2023–2024 to 9.22% in 2024–2025. Infants younger than six months, preterm neonates, and children with congenital heart disease remain the most vulnerable to severe RSV infection. These high-risk groups may warrant prioritization in future immunoprophylaxis strategies.