Changes in Epidemiological Characteristics in Children with Mycoplasma pneumoniae Seropositivity in Southwest China from 2022 to 2023.

Background: Mycoplasma pneumoniae (MP) is an important pathogen responsible for community-acquired respiratory infections in children. Global surveillance during the COVID-19 pandemic revealed a marked decline in MP activity. However, beginning in early summer 2023, multiple regions across China reported an unexpected resurgence of MP infections, highlighting the need for detailed epidemiological analysis. Objective: This study aimed to characterize the epidemiological features of MP seropositivity among children in Chengdu, southwest China, and to compare its patterns between the COVID-19 pandemic and post pandemic periods. Methods: A retrospective analysis was conducted on MP testing data from 39,552 children with acute respiratory infections who were treated at West China Second University Hospital, Sichuan University, between January 2022 and December 2023. Results: Both the number of MP tests conducted and the seropositivity rate were significantly lower during the pandemic period than during the post pandemic phase. Compared with male children, female children were more susceptible to MP seropositivity. In terms of age distribution, seropositivity rates were highest among toddlers (1-3 years) and school-aged children (6-14 years). During the pandemic period (2022), MP antibody-positive cases were observed mainly between January and July, whereas in the post pandemic phase (2023), the epidemic peak shifted from June to December. Conclusions: In this single-centre study in Chengdu, nonpharmaceutical interventions (NPIs) implemented during the COVID-19 pandemic was associated with a marked reduction in MP transmission. After these restrictions were lifted, a rebound in MP antibody positivity was observed among children in Chengdu, compared to the NPI period (2022), the post-NPI period (2023) showed a later seasonal peak, which may represent a delayed return to pre-pandemic patterns. Continuous strengthening of MP surveillance is necessary to provide early warning of potential resurgences and outbreak risks.