[Analysis on the epidemiological characteristics of legionnaires' disease in China based on multi-source data]

Objective: To analyze the epidemiological characteristics of Legionnaires' disease in China based on multi-source data. Methods: Based on the metagenomic next-generation sequencing (mNGS) data of bronchoalveolar lavage specimens collected from a third-party medical testing institution from March 2024 to September 2025, this study aggregated nucleic acid detection data for multiple pathogens from the National Pathogenic Bacteria Identification Network's respiratory syndrome surveillance and conducted a meta-analysis by combining published literature. Descriptive epidemiological methods were used to analyze the demographic characteristics, spatiotemporal distribution, and Legionella species and genotype of Legionnaires' disease in China. Results: By integrating three types of data sources, a total of 1 866 Legionnaires' disease cases were included in the study. Chinese Legionnaires' disease patients were predominantly middle-aged and elderly males, accounting for 64.31% of cases. The age distribution of cases exhibited a bimodal pattern, with a significant concentration in the middle-aged and elderly population. The 60-65 age group had the highest incidence. However, in addition to the peak in the middle-aged and elderly population, there was also a peak in the 0-5 age group. The number of cases showed a peak occurring from July to August. The cases exhibited significant regional distribution disparities across the country. Legionella pneumophila infection was predominant (accounting for 95.70%), with other species including Legionella macleodii (20 cases) and Legionella longbeachae (18 cases). Among 412 samples, L. pneumophila genotypes were obtained, divided into 7 sequence types, including ST36 (n=148), ST1 (n=60), ST23 (n=58), ST51 (n=51), ST734 (n=51), ST42 (n=32), and ST47 (n=12). The distribution of STs in different geographical regions had commonalities, but there were also certain regional differences. The results of universal core genome multi-locus sequence typing showed that each ST formed relatively independent branch clusters, indicating clear genetic differentiation between different STs. The overall genetic diversity of Legionella in China was high. Conclusion: Legionella-positive cases have been detected throughout the year in China, with a wide distribution and regional differences. L. pneumophila has a high proportion and a large genetic diversity in its genome.