Between 1 January and 31 December 2023, a total of 19,955 dengue fever cases were reported, including 8,275 confirmed cases, 11,659 probable cases, and 21 suspected cases. Of the 19,934 confirmed and probable cases, there were 14,585 indigenous cases, 3,632 domestic imported cases, 1,579 overseas imported cases, and 138 other cases (including 101 cases with unclear definitions, 30 cases with unknown imports from overseas, and 7 cases from Hong Kong and Taiwan of China). There was one death among domestic imported cases. The time intervals from onset to diagnosis for indigenous cases, domestic imported cases, and overseas imported cases were 3, 4, and 3 days, respectively.
Descriptive study of indigenous dengue cases
Temporal distribution of indigenous dengue cases
Indigenous cases of dengue occurred between June and December. It showed seasonal characteristics, with a peak period from August to October (11,753 cases, 80.6%) and September being the peak month (4,817 cases, 33.0%) (Fig. 1, red colour). The peak period of affected regions (provinces, cities, or counties) was from August to November, with October being the peak month.
Temporal distribution mapping of dengue cases in Chinese mainland, 2023
Spatial distribution of indigenous dengue cases
A total of 14,585 cases were distributed across 140 counties, 54 cities, 10 provinces (Zhejiang, Fujian, Hubei, Hunan, Guangdong, Guangxi, Hainan, Sichuan and Yunnan provinces, and Chongqing Municipality) in the south of the Yangtze River Basin (Fig. 2). The top three areas with cases at the county level were Ruili City, Dehong Dai and Jingpo Autonomous Prefecture, Yunnan Province (3,828 cases, 26.2%); Jinghong City, Xishuangbanna Dai Autonomous Prefecture, Yunnan Province (3,453 cases, 23.7%); and Mengla County, Xishuangbanna Dai Autonomous Prefecture, Yunnan Province (2,209 cases, 15.1%). There were 10,268 cases in the Yunnan Province, accounting for 70.4% of the cases, which were mainly distributed along the southwest border. Additionally, there were 3,756 cases in Guangdong Province (25.8%), mainly distributed in southern coastal areas, with 45.5% in Guangzhou City.
Spatial distribution of indigenous dengue cases in Chinese mainland, 2023
Monthly spatial emerging of indigenous dengue cases
Indigenous cases emerged from low latitudes along the southwestern border and the southern and southeastern coastal areas to high latitudes in the central region from June to September and mainly emerged from low latitudes subsequently (Fig. 3). In June, five counties were affected in the Yunnan, Guangdong, and Fujian provinces. In July, nine counties were newly affected in the Zhejiang, Fujian, Guangdong, and Yunnan provinces. In August, 22 counties were newly affected in Zhejiang, Fujian, Hubei, Hunan, Guangdong, Hainan, and Yunnan provinces. In September, 55 counties were newly affected in the Zhejiang, Fujian, Hubei, Hunan, Guangdong, Hainan, Sichuan and Yunnan provinces, and Chongqing Municipality. In October, 37 counties were newly affected in the Zhejiang, Fujian, Hubei, Guangdong, Hainan, and Sichuan provinces. In November, 11 counties were newly affected in the Guangdong, Sichuan, and Yunnan provinces. In December, one county was newly affected in Guangdong Province.
Monthly spatial emerging of indigenous dengue cases in Chinese mainland, 2023
Demographic distribution of indigenous dengue cases
The male-to-female ratio of indigenous cases was 1.1:1. The top four age groups with the highest number of indigenous cases were 35–44 years (17.9%), 45–54 years (17.9%), 25–34 years (17.6%), and 55–64 years (16.1%), with a total of 69.5% in the 25–64 age group. The top four occupations with the highest number of indigenous cases were farmer (24.5%), households or the unemployed (18.3%), and businesspeople (10.8%), accounting for 53.6%. See Table 2.
Descriptive study of domestic imported dengue cases
Origins and distributions of domestic imported dengue cases
Among the 3,632 domestic imported cases in Chinese mainland in 2023, 1,112 cases (30.6%) were transmitted between provinces, 1,772 cases (48.8%) were transmitted between different cities within the province, and 748 (20.6%) were transmitted between different counties within the city. A total of 3,632 domestic imported cases from 45 counties, 28 cities, and 10 provinces were imported into 579 counties, 179 cities, and 28 provinces among the 31 provinces in Chinese mainland (except Tianjin Municipality, Heilongjiang Province, and Tibet). The origins were mainly Yunnan, Guangdong, and Fujian provinces. The destinations were mainly located in the Yunnan, Guangdong, Zhejiang, Sichuan, and Hunan provinces.
Flow map of domestic imported dengue cases
Of the domestic imported dengue cases, 3,322 (91.5%), 197 (5.4%), and 94 (2.6%) cases were imported from the Yunnan, Guangdong, and Fujian provinces, respectively. Additionally, 19 cases were imported from Zhejiang, Hubei, Hunan, Guangxi, Hainan and Sichuan provinces, and Chongqing Municipality (Fig. 4A). Overall, 3,322 domestic imported cases from Yunnan Province showed a radial output, with 69.7% imported into local cities or counties in Yunnan Province and 30.3% imported into 27 other provinces, including 19.3% imported into Zhejiang, Guangdong, Sichuan, and Hunan provinces. Of the 197 domestic imported cases from Guangdong Province, 75.6% were imported into local cities or counties within Guangdong Province, and 24.4% were imported into 15 other provinces. Of the 94 domestic imported cases from Fujian Province, 51.1% were imported into local cities or counties within Fujian Province, and 48.9% were imported into 6 other provinces.
Moreover, 2,320, 337, 256, 136, and 125 cases were imported into Yunnan, Guangdong, Zhejiang, Sichuan, and Hunan provinces, respectively (Fig. 4B). A total of 2,320 cases imported into Yunnan Province were from Yunnan Province itself, except for 3 cases. Of the 337 cases imported into Guangdong Province, 50.0% were from Yunnan Province, 44.5% were from Guangdong Province, and the remaining were from Zhejiang, Fujian, Hunan, and Guangxi provinces. Of the 256 cases imported into Zhejiang Province, 86.7% were from Yunnan Province, 9.4% were from Fujian Province, and the remaining were from Guangdong and Sichuan provinces. Of the 136 cases imported into Sichuan Province, 98.5% were from Yunnan Province, and the remaining were from Guangdong Province and Chongqing Municipality. Further, 92.8% of 125 cases imported into Hunan Province were from Yunnan Province, and the remaining were from Guangdong and Fujian provinces.
Flow map of domestic imported dengue cases in Chinese mainland, 2023. A Domestic output flow B Domestic input flow
Demographic distribution of domestic imported dengue cases
The male-to-female ratio of domestic imported cases was 1.2:1. The top four age groups with the highest number of domestic imported domestic cases were 25–34 years (27.6%), 35–44 years (22.1%), 45–54 years (16.0%), and 15–24 years (13.4%), with 79.1% in the 15–54 age group. The four occupations with the highest number of domestic imported cases were farmers (38.2%), households or the unemployed (11.2%), and students (9.8%), accounting for 59.2%. See Table 2.
Descriptive study of overseas imported dengue cases
Temporal distribution of overseas imported dengue cases
Imported cases were reported throughout the year. It showed seasonal characteristics, with a peak period from August to September (1,017 cases; 64.4%) (Fig. 1). The peak period of affected regions (provinces, cities, or counties) was from August to October, with September being the peak month.
Origins and distributions of overseas imported dengue cases
There were 1,579 overseas imported cases from 39 countries and regions, with 1,088 cases from Myanmar (68.9%), 133 cases from Laos (8.4%), and 114 cases from Thailand (7.2%) imported into 255 counties, 125 cities, and 22 provinces. Overseas imported cases were clustered along the southwestern border of Yunnan Province (adjacent to Myanmar, Laos, and Vietnam), the coasts of Guangdong and Fujian provinces, and central Zhejiang Province. The three provinces with the highest number of cases were Yunnan Province (1,175 cases, 74.4%), Guangdong Province (124 cases, 7.9%), and Zhejiang Province (88 cases, 5.6%). Among them, 915 cases (57.9%) were distributed in the Xishuangbanna Dai Autonomous Prefecture on the southwestern border of Yunnan Province.
Sankey diagram of overseas imported dengue cases
This Sankey diagram showed that how overseas imported cases flowed from overseas countries to the provinces in Chinese mainland. It showed not only the numbers of cases (different width) but also the distributions (different colors) (Fig. 5).
Sankey diagram of overseas imported dengue cases in Chinese mainland, 2023
Of the 1,088 cases from Myanmar, 97.4% were imported into Yunnan Province, and the remaining were imported into nine other provinces. Of the 133 cases from Laos, 68.4% were imported into Yunnan Province, and the others were imported into 12 other provinces. In total, 38.6% and 22.8% of the 114 cases from Thailand were imported into Guangdong and Zhejiang provinces, respectively, and the others were imported into another 12 provinces.
Of the 1,175 cases imported into Yunnan Province, 91.1% were from Myanmar, and the remaining were from six countries and regions. A total of 124 cases were imported into Guangdong Province from 24 countries and regions, including Thailand and Malaysia. Additionally, 44 cases were imported into Zhejiang Province from 22 countries and regions, including Thailand and Laos.
Demographic distribution analyses of overseas imported dengue cases
The male-to-female ratio of imported cases was 1.7:1. The four age groups with the highest number of overseas imported cases were 35–44 years (26.2%), 25–34 years (25.9%), 45–54 years (18.2%), and 55–64 years (10.9%), with 80.9% in the 25–64 age group. The two occupations with the highest number of overseas imported cases were farmers (49.3%) and businesspeople (11.9%), accounting for 61.2%. See Table 2.