Twenty-year epidemiological trends of Mycoplasma pneumoniae infection among hospitalized children: age shift and post-COVID resurgence

Background Mycoplasma pneumoniae ( MP ) is a major cause of pediatric respiratory infections, characterized by cyclical epidemics and age- and season-specific patterns. However, long-term epidemiological data spanning multiple epidemic cycles are limited. Methods We conducted a 20-year retrospective study of children (< 18 years) hospitalized with respiratory tract infections and undergoing MP testing at Children's hospital of Soochow University from October 2005 to December 2025. MP infection was defined by positive PCR and/or serological evidence. Positivity was analyzed by age, sex, season, calendar period, and COVID-19 pandemic phase. Results Among 51,399 specimens, 16,086 were MP -positive (31.30%). Epidemic peaks recurred approximately every 3 ~ 5 years. A stable age-dependent gradient was observed, with highest positivity in children ≥ 7 years (51.73%) and lowest in infants < 6 months (12.97%). Despite temporal fluctuations, age-related patterns remained consistent, with a gradual shift toward older age groups. MP demonstrated clear seasonality, predominating in summer and autumn; recent autumn peaks attenuated, whereas summer predominance persisted. During the COVID-19 pandemic, MP positivity declined markedly across all ages, followed by a partial rebound, particularly in children ≥ 3 years. Conclusions Pediatric MP infection exhibits recurrent epidemic cycles, stable age dependency, and evolving seasonal dynamics. Sustained long-term surveillance is essential to inform clinical preparedness and public health strategies. Clinical trial number Not applicable.