Estimating the epidemic size of chikungunya virus infection in Guangzhou, China, from July to September 2025: a single-center cross-sectional study.

Although no previous large-scale outbreak was reported in China in recent years, since July 2025, a surge in the number of chikungunya virus infections has been observed in multiple cities of Guangdong province following the introduction of imported cases, including Guangzhou. Using serological and epidemiological data obtained during a chikungunya outbreak in Guangzhou city, we estimated an attack rate of 22% for chikungunya virus infection. Accounting for case under-reporting is crucial for accurate disease burden assessment and planning of future vaccination programmes.