An exceptionally large wave of M. pneumoniae infections among children in Tianjin post COVID-19 pandemic

Background: The coronavirus disease 2019 (COVID-19) pandemic has caused a persistent lowering of Mycoplasma pneumoniae (M. pneumoniae), which is commonly found in children with respiratory tract infections (RTIs). However, in 2023, we observed an unusually high number of M. pneumoniae infections among children from Tianjin, the second largest city in northern China. This study sought to analyze the epidemiological characteristics of children with RTIs caused by M. pneumoniae in northern China post COVID-19, in order to provide a theoretical basis for clinical diagnosis and treatment. Methods: Between January 2019 and December 2023, a total of 78,886 children with respiratory infections from General Hospital of Tianjin Medical University were included in this study. A rapid immunochromatographic assay kit was used to test for M. pneumoniae specific immunoglobulin M (IgM) in these patients. The relevant clinical data of M. pneumoniae-positive cases were also collected, and analyzed by SPSS software. Results: Out of the 78,886 samples collected, a total of 11,268 tested positive for M. pneumoniae specificIgM antibody. The average positive rate was 14.3% in the past 5 years. In the year 2023 alone, there were 5,870 M. Pneumoniae positive cases, surpassing the combined count from the previous 4 years. The incidence of M. pneumoniae had significantly surged since September 2023, peaking at 1,717 cases in November 2023, with a notable surge during the fourth quarter. The prevalence of M. pneumoniae infection was primarily observed among children aged 4-6 years and 7-9 years both before and during the COVID-19 pandemic; however, a noticeable increase was observed among children aged 10-14 years after the pandemic ended. Boys exhibited a lower positive rate (13.19%) compared to girls (15.56%). In addition, the proportion of pneumonia cases in 2023 was significantly higher than that in previous years (P<0.001). Conclusions: Our study revealed that following a prolonged global lowering of M. pneumoniae since the COVID-19 pandemic, a significant outbreak had emerged in northern China since September 2023. The proportion of M. pneumoniae positive children in the older age group increased in 2023 compared to that observed in 2019. Additionally, there was an increase in the proportion of pneumonia among M. pneumoniae positive cases in 2023 compared to the pre-COVID-19 pandemic period.