Comparative Epidemiology and Transmission Risk Assessment of Imported and Indigenous Dengue Fever at the National and Selected Provincial Levels, China, 2005–2025

Introduction: This study compared epidemiological characteristics of imported and indigenous dengue fever cases in China from 2005 to 2025 and assessed the dynamic provincial transmission risks. Methods: This study compared the 21-year trends in national surveillance data. It examined temporal changes in the countries of origin of imported cases and the dynamic risk ratio of indigenous to imported cases across ten high-import provinces, as well as the disparity of epidemiological characteristics between imported and indigenous cases. Results: Indigenous cases dominated the epidemic in China (90.1%, 134,129/148,893). Imported cases (9.9%, 14,764/148,893) were the initial trigger, increasing notably before the local epidemic season. They were predominantly men (70.5%) aged 25-49 years, mainly "farmers and workers (38.6%)" and "commercial/service personnel (22.9%)". In contrast, indigenous cases had a balanced sex ratio (1.1:1), and "household/unemployed/retired persons (32.1%)" constituted the largest occupational group. Further spatiotemporal analysis revealed that: 1) The primary source country for imported cases nationwide shifted from Cambodia (41.1%) to Myanmar (29.6%); 2) Imported cases in Yunnan were predominantly from Myanmar (71.1%) and "farmers and workers (50.5%)", whereas in Guangdong, they were more diverse in origin and dominated by "commercial/service personnel (30.2%)"; 3) The risk ratio of indigenous to imported cases across ten provinces exhibited significant heterogeneity: Yunnan and Guangdong were persistent high-risk areas, whereas Sichuan and Jiangsu maintained lower risk. Hunan and Chongqing exhibited high-risk in recent years, with Chongqing's ratio reaching 36.5 in 2025 and Hunan's 15.5 in 2024. Conclusions: The dengue fever epidemic in China was initiated by importation; however, the scale and risk of subsequent local transmission varied significantly and dynamically across provinces. Control strategies should integrate source interception of imported cases with tailored interventions addressing distinct importation profiles, evolving local transmission risks, and population characteristics across provinces.