Surge in <i>Chlamydia pneumoniae</i> infections in China: insights from 2022 to 2024

<i>Chlamydia pneumoniae</i> (<i>C. pneumoniae</i>) remains an underrecognized cause of respiratory infections in China. As <i>C. pneumoniae</i>-associated pneumonia has not been classified as a notifiable infectious disease, nationwide surveillance data are unavailable, resulting in poorly characterized epidemiological patterns. Using targeted next-generation sequencing (tNGS) data from 2,316,182 hospitalized acute respiratory infection (ARI) cases across 315 cities in 31 provinces of mainland China, we characterized the seasonal epidemiology and demographic patterns of <i>C. pneumoniae</i> infections. Our analyses revealed a 4.3-fold increase in <i>C. pneumoniae</i> positivity rates in 2024; from 0.21% in 2022-2023 to 0.90% in 2024, with distinct geographic clustering in the southwestern regions of the Yangtze River Basin. Seasonal analysis identified the period from April to June as the peak season for <i>C. pneumoniae</i> infections. Demographic stratifications showed male adolescents aged 10-19 years emerged as the highest-risk population, while women aged 25-44 years also showed elevated infection risks likely due to caregiving roles. Our findings demonstrate the changes in the epidemiology of <i>C. pneumoniae</i> in post-pandemic China and underscore the necessity of enhancing surveillance of <i>C. pneumoniae</i> infections and implementing targeted prevention strategies, particularly in high-burden areas and high-risk populations such as adolescents/caregivers in southwestern regions of the Yangtze River Basin.