Epidemiology and co-infection networks of pediatric respiratory pathogens in eastern China after COVID-19 restriction relaxation: a retrospective study

Objectives: To characterize the epidemiology, seasonal fluctuations, and co-infection networks of pediatric respiratory pathogens in eastern China following the relaxation of COVID-19 non-pharmaceutical interventions (NPIs). Methods: We conducted a retrospective analysis of 7,473 throat swab samples collected from children (≤18 years) presenting with acute respiratory tract infections (ARTIs) at a tertiary hospital in Nanjing between January 2024 and May 2025. Samples were tested for 13 common pathogens using a multiplex RT-PCR assay. Pathogen detection rates, temporal trends, and co-infection dynamics were analyzed using Kruskal-Wallis tests, time-series smoothing, and network analysis. Results: dominated in mid-summer (22.8% in August 2024), and RV maintained high year-round activity. Co-infections occurred in 17.5% of positive samples, with M. pneumoniae-RV and Adenovirus-RV being the most frequent combinations. Network analysis identified RV and M. pneumoniae as central connectors within the intricate co-infection landscape. Conclusions: Pediatric respiratory pathogens have returned with strong, age-specific patterns in post-NPI eastern China. The pronounced "immunity debt" among preschoolers and the high rate of co-infections underscore the urgent need for enhanced multiplex surveillance and the expansion of vaccination programs for RSV and influenza.