In the shadow of COVID-19: changes in the seroprevalence of pediatric Mycoplasma pneumoniae

Mycoplasma pneumoniae (MP) is a leading cause of respiratory tract infections in children. The coronavirus disease 2019 (COVID-19) pandemic has significantly heightened global attention to respiratory infections, including MP. This retrospective study analyzed the MP seroprevalence among children with acute respiratory tract infections (ARTIs) in Nantong, China, across different phases of the COVID-19 pandemic to assess the changes in the epidemiological landscape of MP in children. This study retrospectively analyzed MP-IgM antibody test data from 56,411 children aged 0–14 years with ARTIs at the Affiliated Maternity and Child Health Care Hospital of Nantong University between April 2018 and September 2024. The study period was divided into three phases: pre-pandemic (April 2018–January 2020), pandemic (January 2020–January 2023), and post-pandemic (January 2023–September 2024). Chemiluminescent immunoassay (CLIA) was used to detect serum MP-IgM antibodies, and comparisons were made across the three phases regarding the sex distribution, age distribution, positivity rates, antibody titers, and temporal distribution patterns. The overall MP-IgM positivity rate was 33.39% (18,833/56,411). Positivity rates exhibited a “V”-shaped fluctuation across the three phases, with rates of 39.70% (6,038/15,209) pre-pandemic, 30.12% (6,553/21,758) during the pandemic, and 32.10% (6,242/19,444) post-pandemic (χ²=391.564, P < 0.001). Significant differences in positivity rate distribution occurred among age groups, with the highest positivity rates in the 3 ~ < 6 years group. In the post-pandemic phase, there was a marked increase in infection rates in the ≥ 6 years group (P < 0.001). There were significant differences in the monthly MP positivity rates every year but 2022 (P < 0.05). Significant fluctuations in MP-IgM antibody titers were observed across phases, with the median titer decreasing from 1.80 (IQR: 1.22–3.18) COI pre-pandemic to 1.65(IQR: 1.18–2.67) COI during the pandemic, and subsequently rebounding to 2.16(IQR: 1.31–4.30) COI post-pandemic (H = 368.022, P < 0.001). The epidemiological pattern of MP was significantly altered by the COVID-19 pandemic. The rebound in MP infection rates and the marked increase in antibody titers post-pandemic suggest the need to adjust control strategies for pediatric respiratory infections to address shifts in the patterns of MP epidemics. Moreover, the dynamic changes in MP-IgM titers provide novel insights into the evolution of immune responses.