Objective To analyze the epidemiological characteristics (temporal, spatial, and demographic distributions) of indigenous and imported cases of dengue fever reported in Chinese mainland from 2005 to 2020.Methods The seasonal characteristics of dengue fever were analyzed using Excel 2010. Trend analysis was performed on the annual median age of disease onset using the Mann-Kendall test with the use of R 4.0.2. The map visualization and spatial analysis of cases were conducted using ArcGIS 10.3 software.Results A total of 81 648 indigenous cases of dengue fever were reported in 14 provinces (autonomous regions or municipalities) of Chinese mainland from 2005 to 2020. The indigenous cases were reported between May and December, concentrated between August and November (98.26%), and were distributed south from 35°36?N, mainly in Guangdong (74.01%) and Yunnan (13.74%) provinces, indicating seasonal and regional characteristics. Two major outbreaks of dengue fever occurred in 2014 and 2019, with 46 033 and 15 376 indigenous cases, respectively, adding up to 75.21% of the total indigenous cases. Among the local cases from 2005 to 2020, the male-to-female ratio was 0.99∶1; 54.93% were aged between 25 and <55 years; the top three frequent occupations were engagement in housework or unemployment (21.40%), service workers (12.46%), and retirees (11.71%). The median age of the total indigenous cases was 40 years (interquartile range [IQR]: 27-54). The difference of overall trend of the median age of indigenous cases since 2005 was not statistically significant (Z=1.510, P=0.131). There were a total of 12 701 imported cases in 30 provinces (autonomous regions or municipalities) except the Tibet Autonomous Region in Chinese mainland from 2005 to 2020. The imported cases were reported throughout a year, frequently between June and November (81.81%), and were mainly distributed in Yunnan, Guangdong, Fujian, and Zhejiang provinces, suggesting seasonal and regional characteristics. The imported cases were mainly from Southeast Asian countries including Myanmar and Cambodia. In 2019, the number of imported cases reached a peak of 5 813, accounting for 45.77% of the total imported cases. Among the imported cases from 2005 to 2020, the male-to-female ratio was 2.05∶1; 73.29% were aged between 25 and 54 years; the top three frequent occupations were farmers (24.13%), service workers (19.34%), and engagement in housework or unemployment (13.91%). The median age of the total imported cases was 33 years (IQR: 26-44). The overall trend of the median age of imported cases since 2005 was not statistically different (Z=0.413, P=0.679). A total of 15 376 indigenous cases and 5 813 imported cases reported in 2019, and the number of indigenous and imported cases reported were dramatically decreased to 616 and 158 in 2020, respectively.Conclusions Dengue fever outbreaks in Chinese mainland are still caused by imported cases, with significant seasonal and regional characteristics. The indigenous cases were mainly distributed in Guangdong and Yunnan provinces, while the imported cases were mainly from Southeast Asian countries including Myanmar and Cambodia. There was no significant change in the median age of dengue fever cases from 2005 to 2021.
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