Objective To analyze the epidemiological characteristics of local cases, cases imported from other provinces, and cases imported from abroad in Class Ⅱ dengue transmission risk fever areas of China from 2005 to 2024.

Methods Based on notifiable infectious disease surveillance data, a general linear regression model was used to analyze long-term trends. The relative importance of Class Ⅱ areas was assessed by excluding Class Ⅰ dengue transmission risk areas and data from 2020−2022. Descriptive epidemiological methods were employed to analyze the distribution characteristics across populations, space, and time.

Results From 2005 to 2024,the proportion of local cases occurring in Class Ⅱ areas (relative to non-Class Ⅰ areas) increased significantly at a rate of 2.52 percentage points per year (β=2.52, P<0.001). Population distribution analysis revealed that local cases in provinces like Shandong, Henan, and Hubei were primarily elderly farmers; in Jiangxi and Chongqing, local cases were predominantly housewives or unemployed women; meanwhile, imported cases were mainly young and middle-aged males. Spatial distribution revealed three patterns: Hunan faced overlapping triple risks (local, other provinces, and abroad); Chongqing and Jiangxi were dominated by local transmission; Sichuan served as a major gateway for overseas imported cases. Temporal distribution exhibited a three-phase pattern: imported cases (71.43%−95.56% from abroad) dominated from January to July; local outbreaks began in August (local cases accounted for 94.77% of August cases in Jiangxi);and domestic imported cases intensified after September (cases imported from other provinces accounted for 70.63% of October cases in Hunan).

Conclusion Between 2005 and 2024, the risk of dengue transmission in Class Ⅱ regions of China has been continuously increasing, with epidemic characteristics exhibiting significant regional heterogeneity and seasonal patterns. Imported cases were predominantly observed among young and middle-aged males, while local cases in Shandong, Henan, and Hubei were mainly elderly farmers. In Jiangxi and Chongqing, the majority were unemployed individuals and homemakers. Temporally, the seasonal pattern showed imported cases before summer and autumn, local outbreaks in August, and increased interprovincial transmission in autumn. Therefore, it is urgent to establish a precise prevention and control system tailored to regional epidemic characteristics. By implementing region-specific early warning, category-based interventions, and time-phased strategies, the effectiveness of dengue fever prevention and control can be comprehensively enhanced.