Epidemiological Trend of RSV Infection Before and During COVID-19 Pandemic: A Three-Year Consecutive Study in China.

Objective: This study aimed to explore the epidemiological trend and clinical characteristics of respiratory syncytial virus (RSV) infection among inpatient children with lower respiratory tract infection (LRTI) before and during the coronavirus disease 2019 (COVID-19) pandemic. Methods: A retrospective study of inpatients with LRTI was conducted at the Department of Pulmonology, The Children's Hospital, Zhejiang University School of Medicine (Hangzhou, China) from January 2019 to December 2021. All respiratory specimens were tested for common respiratory pathogens. The clinical data in children with RSV-induced LRTI in the past three years were collected and analyzed. Results: A total of 11,290 patients were enrolled, and RSV positive cases were 402 (7.6%), 288 (9.6%), 415 (13.8%) in 2019, 2020, 2021, respectively, with a significant statistical difference of the RSV positive rate among the three groups (p < 0.001). Most patients were under 2-year old, especially under 1-year old, and the median age of patients was 4 months, 5 months, 6 months in 2019, 2020, 2021, respectively, with a tendency to increase in age. In terms of the seasonal distribution, most patients of LRTI with RSV infection were admitted in winter, while in 2021 compared with in 2019, the cases significantly reduced in winter and increased in autumn. From 2019 to 2021, there was an increase in autumn trend year by year. Conclusion: RSV infection was still an important cause of hospitalization in children with LRTI after the outbreak of COVID-19, and its proportion increased gradually. LRTI caused by RSV is still more common in infants under 1-year old, but there is a trend of increasing in older children. What deserves the attention of pediatricians and Center for Disease Control is that the incidence of RSV infection continues to rise in autumn, and the difference in seasonal distribution is narrowed.