Spatiotemporal analysis of indigenous and imported dengue fever cases in Guangdong province, China

Abstract

Background: Dengue fever has been a major public health concern in China since it re-emerged in Guangdong province in 1978. This study aimed to explore spatiotemporal characteristics of dengue fever cases for both indigenous and imported cases during recent years in Guangdong province, so as to identify high-risk areas of the province and thereby help plan resource allocation for dengue interventions.

Methods: Notifiable cases of dengue fever were collected from all 123 counties of Guangdong province from 2005 to 2010. Descriptive temporal and spatial analysis were conducted, including plotting of seasonal distribution of cases, and creating choropleth maps of cumulative incidence by county. The space-time scan statistic was used to determine space-time clusters of dengue fever cases at the county level, and a geographical information system was used to visualize the location of the clusters. Analysis were stratified by imported and indigenous origin.

Results: 1658 dengue fever cases were recorded in Guangdong province during the study period, including 94 imported cases and 1564 indigenous cases. Both imported and indigenous cases occurred more frequently in autumn. The areas affected by the indigenous and imported cases presented a geographically expanding trend over the study period. The results showed that the most likely cluster of imported cases (relative risk = 7.52, p < 0.001) and indigenous cases (relative risk = 153.56, p < 0.001) occurred in the Pearl River Delta Area; while a secondary cluster of indigenous cases occurred in one district of the Chao Shan Area (relative risk = 471.25, p < 0.001).

Conclusions: This study demonstrated that the geographic range of imported and indigenous dengue fever cases has expanded over recent years, and cases were significantly clustered in two heavily urbanised areas of Guangdong province. This provides the foundation for further investigation of risk factors and interventions in these high-risk areas.

Figure 1

The population density at the county level, Guangdong province, China, 2010.

Figure 2

The seasonal distribution of indigenous and imported dengue fever cases in Guangdong province, China, 2005–2010.a. Seasonal distribution of indigenous cases; b. Seasonal distribution of imported cases. The Boxplots display the values of the 25th, 50th, 75th percentiles. The whiskers extend to the most extreme data point < 1.5 times the inter-quartile range.

Figure 3

The geographic distribution of cumulative incidence by county in Guangdong province, China, 2005–2010.

Figure 4

The geographic changing on the affected counties by the imported and indigenous dengue cases in Guangdong province, China, 2005–2010.

Figure 5

The clusters of dengue fever by all, indigenous and imported cases in Guangdong province, 2005–2010.a. Two identified clusters of imported and indigenous dengue fever cases (maximum spatial cluster size ≤ 50% total population); b. Two identified clusters of indigenous dengue fever cases (maximum cluster spatial size ≤ 50% total population); c. One identified cluster of imported dengue fever cases (maximum cluster spatial size ≤ 50% total population); d. Three identified subclusters of imported dengue fever cases (maximum cluster spatial size ≤ 10% total population).