Drivers of respiratory infection landscapes in the post-pandemic era - The interplay of age, seasonality, and inter-annual variability in pathogen distribution: A retrospective surveillance study.

ObjectiveTo evaluate pathogen spectrum and epidemiological dynamics of acute respiratory infections (ARI) in Nankai District, Tianjin, during the post-pandemic era (2024-2025).Study designRetrospective surveillance study.MethodsA total of 1853 ARI specimens were retrospectively collected from two sentinel hospitals during weeks 1-52 of 2024-2025. Multiplex PCR was used to detect 31 pathogens. Statistical analyses were performed using SPSS 25.0.ResultsThe overall positivity rate was 39.61% (734/1853). Viral pathogens predominated (66.02%), followed by bacterial (23.53%) and atypical pathogens (10.45%). The top five pathogens were SARS-CoV-2 (8.90%), Haemophilus influenzae (6.31%), influenza A H3N2 (5.02%), Mycoplasma pneumoniae (4.75%), and influenza A H1N1 (3.99%). Males showed higher co-infection rates than females (P = 0.020). Positivity rates were highest in the 35-59 (48.19%) and 18-34 age groups (47.43%). M. pneumoniae primarily affected children aged 4-17 years, whereas SARS-CoV-2 was more prevalent in adults. Spring and winter exhibited the highest positivity rates, with summer the lowest (22.17%). Significant inter-annual differences were observed (P