Positive Rates of Mycoplasma Pneumoniae Antibodies in Children Before, During and After COVID-19 Outbreak: an observational study in Chengdu, China from 2017 to 2024

Luoman Yan^1,2Hao Dong^1,2Haiyan Zhang^2,3Zixi Du^1,2Lei Zhang^1,2*Meimei Lai^1,2*

• ¹University of Electronic Science and Technology Hospital, Chengdu, China
• ²Chengdu Women and Children's Central Hospital, Chengdu, China
• ³Southwest Medical University, Luzhou, China

Mycoplasma pneumoniae (M. pneumoniae) is a leading pathogen of pediatric pneumonia, yet its epidemiological profile in Chengdu remains understudied. This study aimed to analyze the epidemiological trends of M. pneumoniae antibody positive rates among children in Chengdu from 2017 to 2024, encompassing periods before, during, and after the COVID-19 pandemic, and to assess associated changes in respiratory disease patterns. We retrospectively analyzed clinical diagnoses and M. pneumoniae antibody test results from 222,364 children with respiratory infections treated in the emergency, outpatient, and inpatient departments of Chengdu Women and Children's Central Hospital (January 2017–December 2024). Local temperature and humidity data were concurrently collected. Epidemiological trends in M. pneumoniae antibody positive rates were evaluated by year, sex, age, season, and climate parameters, alongside shifts in respiratory disease composition among M. pneumoniae -positive children. The M. pneumoniae antibody positive rates exhibited an overall upward trend, with three epidemic peaks (2017, 2019, and 2023–2024) and a notable decline during the pandemic. Females showed higher susceptibility than males. Outpatients aged 3–6 years and inpatients aged 0–3 years were most vulnerable pre-pandemic; however, post-pandemic, M. pneumoniae antibody positive rates increased with age (0–6 years). Seasonal peaks typically occurred in autumn, but during the mid-to-late pandemic, winter-autumn alternation was observed. Early-pandemic humidity positively correlated with M. pneumoniae antibody positive rates. Post-pandemic, asthma replaced post-infection cough as the third most common outpatient diagnosis, while inpatient diagnoses were dominated by pneumonia and severe pneumonia, the latter showing a significant rise in proportion. Following the COVID-19 pandemic, a substantial increase of Mycoplasma pneumoniae (M. pneumoniae) antibody positive rates was observed among pediatric populations in Chengdu beginning in 2023. This study presents a descriptive analysis of serum antibody detection results, offering baseline epidemiological data to inform prevention and control strategies for M. pneumoniae infections among children in the Chengdu region.