The ecological factors contributing to the chikungunya outbreak in Ruili, a border city in Yunnan Province, China

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BACKGROUND: Chikungunya virus (CHIKV), an arthropod-borne pathogen, has caused recurrent epidemics in tropical and subtropical regions, as well as sporadic outbreaks in certain temperate areas, posing significant public health challenges. The globalization-driven increase in international tourism and trade has facilitated the spread of the virus, leading to several outbreak events in China triggered by imported cases, including the 2019 outbreak in Ruili City, Yunnan Province. METHODS: This study conducts a quantitative analysis of the spatiotemporal patterns of outbreak in Ruili City and investigates the impact of ecological factors on the occurrence of local chikungunya cases and the extent of its autochthonous transmission, using panel logistic regression and Poisson regression models, respectively. RESULTS: This outbreak began on September 20, 2019, and lasted for approximately twelve weeks, during which a total of 139 local infections and 31 imported infections were reported. The peak incidence occurred in the third week of the outbreak, after which a gradual decline was observed. Most cases were concentrated in five specific townships located in close proximity to the Jiegao Port. Modeling analysis revealed that the presence of imported cases, population density, and the percentage coverage of grassland were the most significant factors influencing autochthonous transmission of CHIKV, significantly influencing both the occurrence of local chikungunya cases and the extent of autochthonous transmission. Furthermore, the occurrence of local cases was positively associated with the presence of local cases reported in the previous week and precipitation levels in the week before last. CONCLUSIONS: Our findings suggest that autochthonous transmission of chikungunya fever following case importation is significantly associated with imported case, high population density, and areas with great grassland coverage. A comprehensive understanding of the factors facilitating autochthonous transmission can enhance future surveillance efforts, environmental management strategies, and disease control measures for chikungunya fever.

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