Epidemiology, transmission, vector and factors analysis of chikungunya outbreak in 2025, Quanzhou City of China.

BACKGROUND: Following a major chikungunya outbreak in Foshan City, China, locally transmitted cases have been reported across the country. Research remains limited to epidemiology, transmission dynamics, vector characteristics, and risk factors of chikungunya fever. METHODS: We analyzed 164 chikungunya cases reported in Quanzhou City, Fujian Province, between August 18 and September 9, 2025, along with mosquito surveillance data collected from August 25 to September 13, 2025. We examined case characteristics, symptom patterns, Cycle threshold (Ct) values trends, and vector distributions. Logistic regression was used to identify demographic factors and mosquito density indices associated with infection risk. RESULTS: Among 164 cases, 50.0% were male and 38.4% were aged ≥ 60 years. Ct values were significantly influenced by age (p = 0.0044) and the onset-to-diagnosis intervals (p < 0.0001), but not by symptom patterns. Advanced age was a major risk factor, particularly for individuals aged 70-89 years (OR = 6.18, 95% CI = 4.08-8.98) and those 90 years or older (OR = 4.37, 95% CI = 1.36-10.29). Higher mosquito larval and adult densities also increased infection risk. Following implementation of emergency response protocols and intensive mosquito control measures, zero incident cases were reported within 21 days. CONCLUSION: Chikungunya disproportionately affects older adults, especially those aged ≥ 70 years. Viral load increases with age and decreases with delayed diagnosis. The lack of correlation between symptoms and viral load may suggest that asymptomatic individuals could be equally infectious, providing guidance for the screening and management of high-risk populations.