Clinical epidemiology and viral genomics insights from a Chikungunya fever outbreak in South China, 2025.

Background: Chikungunya fever (CHIKF) is a mosquito-borne viral disease characterized by fever, rash, and severe joint pain. However, these classical descriptions are based overwhelmingly on the Indian Ocean and Caribbean lineages. With the recent introduction and spread of the Middle Africa lineage (MAL) into Asia, understanding its clinical presentation in new populations, such as Chinese, has become a public health priority. Whether the recently introduced MAL causes comparably severe disease in China remains unknown. Methods: We enrolled 415 laboratory-confirmed cases of Chikungunya virus (CHIKV) infection during an outbreak in Foshan, China. Clinical manifestations, laboratory parameters, and whole-genome sequencing data were integrated to quantify the symptom burden from three different perspectives using multivariate logistic regression, and to trace the viral source via maximum-likelihood phylogenetic analysis. Results: Compared with the classical phenotype, the MAL outbreak in China was appreciably milder. The most common clinical manifestations were arthralgia (83.61%), fever (74.46%), and rash (61.93%). Multivariate logistic regression showed that older age (OR = 0.979, P = 0.029) and male sex (OR = 0.528, P = 0.038) were negatively correlated with the occurrence of higher symptom burden, while prolonged fever (OR = 8.156, P < 0.001) was a significant risk factor. Reduced estimated glomerular filtration rate and thrombocytopenia were associated with longer disease duration. Phylogenetic analysis revealed that the outbreak-associated CHIKV strains belonged to MAL and harbored the E1-A226V and E2-I211T mutations. Conclusion: These findings provide an evidence base for clinical management and prognostic assessment during CHIKF outbreaks and underscore the importance of monitoring laboratory parameters alongside molecular surveillance.