Estimating the transmissibility of the 2025 chikungunya fever outbreak in Foshan, China: a modelling study

Between June 16 and July 31, 2025, cumulative cases reached 2658, with 92.96% concentrated in the Shunde District. Model simulations showed that a cumulative case count is consistent with local reports (Pearson r = 0.99, P < 0.001). The median overall <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>R</mml:mi> <mml:mn>0</mml:mn></mml:msub> </mml:math> of this outbreak was 7.2807 [interquntile range (IQR): 7.2809‒7.2811], suggesting sustained transmission. Human-to-mosquito transmission (Median: 22.79, IQR: 5.44‒40.14) had a higher median <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>R</mml:mi> <mml:mn>0</mml:mn></mml:msub> </mml:math> than mosquito-to-human transmission (Median: 2.33, IQR:0.58‒4.07) (Mann-Whitney U P < 0.001). Symptomatic infections (Median: 19.60, IQR: 4.68‒34.52) had a higher median <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>R</mml:mi> <mml:mn>0</mml:mn></mml:msub> </mml:math> than asymptomatic infections (Median: 3.19, IQR: 0.76‒5.62) (Mann-Whitney U P < 0.001). The model simulated cumulative cases were sensitive to parameters <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>a</mml:mi></mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>b</mml:mi></mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>ω</mml:mi> <mml:mi>m</mml:mi></mml:msub> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>ω</mml:mi> <mml:mi>p</mml:mi></mml:msub> </mml:math> . The overall <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>R</mml:mi> <mml:mn>0</mml:mn></mml:msub> </mml:math> and mosquito-to-human <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>R</mml:mi> <mml:mn>0</mml:mn></mml:msub> </mml:math> were sensitive to parameters <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>a</mml:mi></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>b</mml:mi></mml:math> . The human-to-mosquito and symptomatic human-to-mosquito <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>R</mml:mi> <mml:mn>0</mml:mn></mml:msub> </mml:math> were sensitive to parameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math> , while asymptomatic human-to-mosquito <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>R</mml:mi> <mml:mn>0</mml:mn></mml:msub> </mml:math> was sensitive to parameter <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msub><mml:mi>ω</mml:mi> <mml:mi>p</mml:mi></mml:msub> <mml:mo>'</mml:mo> <mml:mo>.</mml:mo></mml:mrow> </mml:math> CONCLUSIONS: The transmissibility of CHIKV is high. Human-to-mosquito transmission, especially symptomatic infections to mosquito transmission, was the main driver of chikungunya virus transmission. These findings underscore the critical need for enhanced screening of travellers from endemic regions, timely case isolation, and targeted vector control to mitigate autochthonous transmission.