Analysis of the epidemic situation of respiratory pathogens in central and southern China before and after the COVID-19 pandemic

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Background Respiratory tract infection is a common disease leading to pediatric hospitalization, exhibiting different epidemiological trends with seasons and ages. This study retrospectively analyzed the infection status of 12 respiratory pathogens from 2018 to 2023, and examined the changes before and after the COVID-19 pandemic. Methods A total of 51,597 hospitalized children with suspected respiratory tract infection, who underwent multiplex PCR testing in a tertiary hospital in Changsha from 2018 to 2023 were included. Testing items included respiratory syncytial virus, adenovirus, influenza virus, parainfluenza virus, Mycoplasma pneumoniae, Chlamydia pneumoniae, and bacterial culture results, among others. Results The infant group had the highest positive rate at 39.25% (7,729/19,693), and the school-age group the lowest at 25.34% (2,015/7,951) ( P < 0.05). During 2020–2021, pathogen positive rates declined compared with pre-pandemic levels; a peak of FluA, FluB, and PIV1-3 occurred in late 2022. After restriction lifting in 2023, FluA, FluB, PIV1, PIV3, AdV, and RSV all rebounded. Among bacterial pathogens, Streptococcus pneumoniae accounted for 26.35% (2,104/7,983), followed by Haemophilus influenzae (20.11%) and Moraxella catarrhalis (14.93%) ( P < 0.005). Co-infection analysis revealed significant positive interactions among Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii, and between Pseudomonas aeruginosa and A. baumannii/K. pneumoniae ( φ >0.9, P < 0.05). M. pneumoniae was more likely to co-infect with viral than bacterial pathogens. Conclusion Due to the impact of the epidemic, the positive rate and disease spectrum of respiratory pathogens have changed. The pandemic induced an initial suppression followed by a marked resurgence of RSV, influenza, and M. pneumoniae after restrictions were lifted. Segmented regression confirmed RSV exhibited the steepest post-pandemic rebound, and toddlers born during lockdown showed a disproportionate surge in infections, supporting the “immunity debt” hypothesis. These findings underscore the importance of age-specific surveillance for preventing pediatric critical illness.