Study of epidemiological characteristics and viral sources of dengue fever outbreak in Guangxi Zhuang Autonomous Region, 2014

Abstract

Objective: To understand the epidemiological characteristics and viral sources of dengue fever outbreak in Guangxi Zhuang Autonomous Region (Guangxi) in 2014. Methods: A combined analysis of epidemiological characteristics and genetic characteristics were performed in this study. The time, population and area distributions of the cases were analyzed. Serum samples were collected from dengue fever cases to detect NS1 antigen by using commercial ELISA kits according to the guideline of the manufacture. RT-PCR assay was conducted to detect dengue virus in NS1 positive samples. Phylogenetic tree based on E gene sequence of dengue virus were further analyzed. Results: During September-December 2014, an outbreak of dengue fever caused by dengue virus type 1 and 2 occurred in Guangxi, a total of 854 cases were reported without death, including 712 laboratory confirmed cases and 142 clinical diagnosed cases, in which 79.63% (680/854) occurred during 22 September-21 October 2014. All the cases had typical dengue fever symptoms. Most cases occurred in Nanning and Wuzhou, in which 83.61% (714/854) were in age group 15-59 years; 46.60% (398/854) were staff or people engaged in commercial service. A total 526 serum samples were tested for dengue virus serotype by RT-PCR assay. Among 414 positive samples, 345 were positive for dengue virus type 1 (DENV-1) and 69 were positive for dengue virus type 2 (DENV-2), no DENV-3 and DENV-4 were detected. The results of phylogenetic analysis of E gene sequence indicated that the sequences of 99.12%(113/114) of DENV-1 strains in Nanning in China shared 100.00% homology with the isolate (SG EHI D1/529Y13) from Singapore in 2013, which belonged to the genotype Ⅰ; All the DENV-2 isolates from Wuzhou shared 99.80% homology with the isolate (D14005) from Guangdong province, which belonged to genotype Cosmopolitan. Conclusions: The outbreak was caused by DENV-1 from Singapore and DENV-2 from Guangdong province in China. It is necessary to strengthen the surveillance and early warning for imported dengue fever, conduct vector control and improve the diagnosis of suspected dengue fever cases for the effective control of dengue fever outbreak.