Epidemiological survey of an outbreak of dengue fever in Lincang, Yunnan, 2015

Objective To understand the epidemiological characteristics of an outbreak of dengue fever and serotype of dengue virus in Lincang at Sino-Myanmar border area in Yunnan province in 2015. Methods The data about dengue fever cases in Lincang were collected. Serum samples in acute phase were collected from the patients for the detection of the viral nucleic acid with RT-PCR. The phylogenetic tree based on nucleotide sequence of C/PreM gene fragments of dengue viruses was analyzed. Results A total of 211 cases of dengue fever were reported in Lincang in 2015, in which 100 were local cases (47.39%), 111 were imported cases (52.61%), i.e., 110 from Myanmar, 1 from Thailand. The disease mainly occurred in Gengma of Lincang where Aedes aegypti was predominant. Dengue fever mainly occurred during July-November. The majority of patients were aged 20-59 years, the youngest was 2 year-old and the oldest was 81 year-old. The male to female ratio was 1.37:1. The dengue fever cases were mainly distributed in farmers (45.02%) and people engaged in commercial service (19.43%). The median of interval between the onset of illness and diagnosis was 2.75 days. The nucleotide sequences of C/PreM of 7 virus strains were obtained. Phylogenetic analysis indicated that the 7 strains belonged to serotype 1, including 5 local strains and 2 imported strains from northern Myanmar. All the 7 strains shared high homology with the strains from Ruili of Yunnan province in 2014, and Myanmar, Thailand and Cambodia. Conclusion During the outbreak of dengue fever in Lincang in 2015, both local cases and imported cases were detected. Dengue virus serotype 1 circulated both in Myanmar and Lincang of China in 2015. The transmission of dengue fever from northern Myanmar was the main cause of local dengue fever epidemic in Lincang. It is necessary to strengthen the surveillance and management of the imported cases of dengue fever and mosquito control to prevent dengue fever outbreak in Lincang.