Reconstructing the post-pandemic landscape: a retrospective, hospital-based surveillance of respiratory pathogens in hospitalized children in Chenzhou, China, 2021–2025

BACKGROUND & OBJECTIVES: The COVID-19 pandemic significantly altered the global ecology of respiratory pathogens. This study aimed to characterize epidemiological shifts and explore determinants of infection risk among hospitalized children at a single center in Chenzhou, China, during the post-pandemic period. METHODS: A retrospective analysis was conducted using hospital-based surveillance data of acute respiratory infections in children from January 1, 2021, to December 31, 2025. Nasopharyngeal swabs from 42,505 cases were tested via multiplex PCR for 13 common respiratory pathogens. Age-stratified positivity rates were calculated, and multivariable logistic regression models were employed to identify independent risk factors, adjusting for year, season, and sex. RESULTS: The data revealed an altered pathogen landscape. Rhinovirus (RV) was consistently detected at a high frequency, becoming a persistently prevalent agent (annual average positivity: 33.65%). The seasonal peak of influenza A virus (FluA) approached pre-pandemic levels, co-circulating with respiratory syncytial virus (RSV) and parainfluenza virus (PIV) in autumn/winter. Mycoplasma pneumoniae (MP) exhibited a notable epidemic surge in 2023 (16.03%), followed by a rapid decline to 0.56% by 2025. Regression analysis, adjusted for multiple covariates, identified age as a significant independent risk factor and revealed three consistent age-related pathogen patterns: (1) RSV/PIV predominance in infants and toddlers; (2) peak incidence of RV, adenovirus (ADV), and human metapneumovirus (HMPV) in preschool children; and (3) increasing risk of MP and Chlamydia pneumoniae with age. Notably, RSV resurged earlier (2021) than reported in Western countries, and the elevated endemicity of RV was more evident.. CONCLUSION: This retrospective analysis of large-scale surveillance data describes changes in respiratory pathogen ecology among hospitalized children in Chenzhou during the post-pandemic period, characterized by age-dependent patterns and region-specific rebound dynamics. These observed season-age risk patterns may help generate hypotheses for informing clinical stratification and could inform local surveillance efforts, though prospective validation is required before clinical implementation.