Objective: To investigate the epidemiological characteristics and temporal-spatial distribution of Mycoplasma pneumoniae (MP) infections among paediatric inpatients with respiratory tract infections in Tianjin, China, across three distinct phases: pre-pandemic (2017-2019), pandemic (2020-2022) and post-pandemic (2023-2024). The primary hypothesis is that the COVID-19 pandemic altered the epidemiology of MP infections in children.

Methods: Retrospective, single-centre study. Methods: Secondary care paediatric hospital in a metropolitan area. Methods: A total of 60 213 paediatric patients hospitalised with respiratory infections between January 2017 and December 2024 were included. The study population consisted of children aged 0-18 years, with a male-to-female ratio of 1.22:1.00. Selection criteria included children admitted with a diagnosis of respiratory infection, while those with incomplete clinical data or non-respiratory infections were excluded. Methods: The primary outcome was the overall positive detection rate of MP-RNA. Secondary outcomes included annual and seasonal variations in MP-RNA detection rates, differences by sex and age group, and the impact of the COVID-19 pandemic on MP epidemiology. All statistical methods, including those used to control for confounding, involved the use of χ² tests for comparing positive rates between groups.

Results: The overall positive detection rate of MP-RNA among children hospitalised for respiratory infections during the study period was 36.58% (22 023/60 213). The annual MP-RNA-positive detection rates from 2017 to 2024 were as follows: 50.74% (411/810) in 2017, 36.28% (1150/3170) in 2018, 27.41% (1459/5323) in 2019, 10.18% (222/2181) in 2020, 11.42% (928/8129) in 2021, 13.27% (579/4364) in 2022, 28.97% (3064/10575) in 2023 and 55.38% (14 210/25 661) in 2024. The highest annual positivity rate was observed in 2024 (55.38%, 14 210/25 661), while the lowest rate occurred in 2020 (10.18%, 222/2181). Statistical analysis revealed significant differences in MP-RNA detection rates across different years (χ²=8331.511, p<0.001). Furthermore, MP-RNA detection rates varied significantly by sex (p<0.001), age group (p<0.001), month (p<0.001) and season (p<0.001) before, during and after the COVID-19 pandemic.

Conclusions: The COVID-19 pandemic substantially altered MP epidemiology in Tianjin's paediatric population, with infection rates demonstrating a U-shaped trajectory across pandemic phases. School-aged children and females exhibited heightened susceptibility. These temporal and demographic patterns emphasise the necessity of incorporating epidemiological surveillance into diagnostic algorithms for childhood respiratory infections, particularly in post-pandemic settings. Future research should focus on multicentre studies to validate these findings and explore the underlying mechanisms.