Abstract:

Objective To analyze the epidemiological characteristics and emergency response of Chikungunya fever epidemic in Qingxiu District, Nanning City in 2025, so as to provide evidence for the prevention and control of mosquito-borne infectious diseases in urban areas. Methods The data of confirmed Chikungunya fever cases with current residential address in Qingxiu District reported between August 11 and November 6, 2025 were retrieved through the Chinese Disease Prevention and Control Information System. Combined with data from field investigations and response efforts, we analyzed the epidemiological characteristics of the cases, including their spatial-temporal-personal distribution, diagnosis and treatment status, clustering patterns, and source-tracing results, and summarized the implementation of emergency response measures such as case search and management, vector surveillance, and mosquito vector control. Results A total of 341 Chikungunya fever cases were reported in Qingxiu District in 2025, including 287 indigenous cases (84.16%) and 54 imported cases (15.84%). The incidence peaked between August and October (n=333; 97.65%) with a bimodal distribution. Geographically, indigenous cases were predominantly clustered in the three subdistricts of Jianzheng, Nanhu and Xinzhu in the downtown area (n=243; 84.67%). The male-female sex ratio of indigenous cases was 1.05∶1, with the majority aged 60 years and above (n=75; 26.13%), and administrative staff constituted the leading occupational group (n=60; 20.91%). Among imported cases, the male-female sex ratio was 1.57∶1, dominated by patients aged 20-39 years (n=18; 33.33%), and students ranked first by occupation (n=13; 24.07%). Most cases were identified via voluntary medical consultation (n=314; 92.08%). Joint pain served as the most common initial symptom at first consultation (n=145; 42.52%), and 29.33%（100/341） of patients presented with the classic triad of fever, rash and arthralgia. Among all confirmed cases, 284 (83.28%) had verifiable spatiotemporal exposure history or epidemiological links to confirmed patients. Fifteen community-based clustered outbreaks were identified, all resulting from community transmission, involving 162 indigenous cases (47.51%). Source-tracing confirmed Shiyou Residential Quarter in Jianzheng Subdistrict as a critical high-risk site for the early transmission of this epidemic. During emergency response, whole-genome sequencing of viruses revealed high homology among the 13 isolated viral strains, with sequence similarities over 99.00% when compared with the viral strains circulating in Guangdong Province. Household screening was implemented across 490 residential compounds within the core epidemic zones, which achieved an effective household rate of 89.32% (50 678 /56 740). A total of 1 961 high-risk individuals were screened, with a positive detection rate of 1.38% (27/1 961). Vector surveillance indicated that the initial Breteau index (BI) at some epidemic foci in the core area exceeded the safety threshold, and the BI values of 95.48% of theaffected sites fell below the safety threshold after targeted interventions. Aedes albopictus was identified as the dominant mosquito species, and no Aedes aegypti was found. Sustained disinfection and vector control efforts were carried out at 444 priority sites across the whole district, which covered a total area of 21.509 6 million square meters. Conclusion Chikungunya fever epidemic in Qingxiu District in 2025 was featured by community-clustered indigenous transmission and closely linked to imported cases from Guangdong Province. Failure in timely identification of early importation sources suggests that it is essential to improve the sensitivity of hospital-based syndrome surveillance. Meanwhile, active case finding, breeding site elimination and targeted vector control should be prioritized as core strategies for prevention and control of Chikungunya fever in urban areas.

Key words: Chikungunya fever, Indigenous cases, Imported cases, Surveillance, Outbreak, Epidemiological characteristics