Epidemic dynamics and age-specific distribution of respiratory pathogens: a direct-to-consumer surveillance study in four regions of China, October 2023–February 2025

OBJECTIVE: This study characterizes the epidemiological features of key respiratory pathogens across four regions of China following the COVID-19 pandemic, aiming to enhance understanding of post-pandemic circulation patterns and supporting the development of targeted prevention strategies. METHODS: Surveillance data on seven respiratory pathogens were collected (October 2023-February 2025) using a direct-to-consumer (DTC) testing approach. Demographic distributions, temporal trends, pairwise correlation analyses and symptom profiles were assessed. RESULTS: Respiratory syncytial virus (RSV) and human rhinovirus (HRV) exhibited a child pattern. Influenza B virus (IFV-B), human adenovirus (HAdV), and Mycoplasma pneumoniae (M. pneumoniae) demonstrated a school-age child pattern. In contrast, influenza A virus (IFV-A) and SARS-CoV-2 showed an elderly pattern. The epidemic patterns of pathogens were categorized into seasonal and year-round circulation. Correlation analyses revealed positive pairwise correlations between IFV-A and RSV, and between HRV and M. pneumoniae, while a negative correlation was observed between IFV-A and SARS-CoV-2. Clustering analysis based on symptom profiles identified three distinct categories: an upper respiratory tract symptom cluster (RSV, HRV), a systemic and respiratory symptom cluster (influenza viruses, SARS-CoV-2), and a systemic symptom cluster (HAdV, M. pneumoniae). Analysis of typical symptom (fever, cough, throat pain) co-occurrence for the seven pathogens showed that only IFV-A (50.14%) met the current Chinese respiratory pathogen surveillance case definition (fever with cough or throat pain); for the other six pathogens, the proportion was below 50%. CONCLUSIONS: Pathogen distribution exhibited significant age-specific variation. The seasonality of different pathogens exhibited regional variations, providing valuable references for future preventive interventions. Notably, half of the individuals with single-pathogen detection reported symptoms that did not meet the current influenza-like illness (ILI) surveillance criteria. Therefore, case definitions should be optimized according to pathogen type in future surveillance efforts.