The cross-city mobility patterns and incubation period of the early-stage chikungunya fever outbreak in Guangdong Province, China, in 2025

Abstract

Background: Chikungunya fever (CF), an arthropod-borne disease caused by Chikungunya virus (CHIKV), is a serious public health threat globally. In July 2025, an outbreak occurred in Foshan City, Guangdong Province, China. A large number of these cases involved cross-city movements, which complicated containment efforts and provided a unique opportunity to study transmission patterns and key epidemiological parameters. Methods: We obtained information on 400 confirmed cases of CF with cross-city exposure histories reported across Guangdong Province in southern China by 21 August 2025. Demographic, clinical, and mobility data were mainly obtained from the National Notifiable Infectious Disease Reporting System and supplemented by epidemiological investigations. The incubation period was estimated using a parametric accelerated failure time model, with log-normal, gamma, Weibull, and Erlang distributions used to fit the model. Subgroup analysis was performed based on mobility patterns and exposure windows. Principal findings: Significant demographic differences were observed compared with local Foshan cases: cross-city cases had higher proportions of males (58.3%), individuals within the age groups of 15–24, 25–34, and 35–44, and individuals with occupations of general staff/workers, business/service workers, and students. Fever (86.4%), arthralgia (79.3%), and rash (61.2%) were the most common symptoms. Mobility analysis revealed that Foshan and Guangzhou were the major sources of infection, with cases spreading mainly to cities within the Pearl River Delta and provinces such as Guangxi (43.3%) and Hunan (15.4%). The median incubation period was estimated to be 5.4 days (95% CI 5.0–5.7), with 2.5th and 97.5th percentiles of 2.5 days and 11.4 days, respectively. Conclusions: This study underscores the central role of population mobility in the spread of CHIKV and highlights distinct epidemiological characteristics of cross-city cases. The estimated median incubation period of 5.4 days provides important evidence for surveillance and response strategies during chikungunya outbreaks. Notably, students and migrant workers accounted for a higher proportion of cross-city cases, suggesting that highly mobile populations may contribute to inter-regional transmission. These findings highlight the importance of strengthened surveillance and coordination across regions for the prevention and control of future outbreaks in Guangdong and other high-risk areas in China.