Spatiotemporal dynamics of the unprecedented chikungunya outbreak in Guangdong, China

ABSTRACT

In 2025, Guangdong province, China, experienced an unprecedented autochthonous chikungunya outbreak associated with a cluster of imported cases. We analyzed weekly city-level surveillance data and found that the outbreak exhibited a distinct two-peak pattern, with an initial outbreak in Foshan city followed by a larger outbreak in the neighbouring city of Jiangmen, together contributing more than 80% of the 23,464 confirmed cases reported in Guangdong. Space-time analysis identified five significant clusters, including two single-city hotspots corresponding to Foshan (July 20–August 16) and Jiangmen (September 14–October 18), suggesting a possible spatial shift in epidemic hotspots over time. In addition, we analyzed daily district-level surveillance data from Foshan and Jiangmen and fitted exponential models to the declining phase of the epidemic. The estimated decay rates were −0.118 in Foshan and −0.142 in Jiangmen, corresponding to epidemic half-lives of 5.87 and 4.88 days, respectively. Overall, our study characterizes the spatiotemporal dynamics of the largest chikungunya outbreak documented in China to date and underscores the importance of strengthening surveillance of mosquito-borne viruses given their increasing transmission risk and complex transmission dynamics.

Chikungunya fever is an acute infectious disease caused by the chikungunya virus and primarily transmitted by Aedes aegypti and Aedes albopictus mosquitoes [1]. It is endemic in tropical regions, including South America, South Asia, and Africa. In 2025, a resurgence of chikungunya fever was reported in several countries that had not reported substantial case numbers in recent years [2]. From January to September 2025, a total of 445,271 suspected and laboratory-confirmed chikungunya cases and 155 deaths were reported globally, including autochthonous and imported cases [2]. As a substantial proportion of asymptomatic infections are unreported, the true burden of disease is likely underestimated [3].

On July 9, 2025, a chikungunya outbreak associated with a cluster of imported cases was identified in Foshan city, Guangdong province, China [4], followed by autochthonous transmission across Guangdong and to other provinces [2]. Between July 20 and December 27, a total of 23,464 laboratory-confirmed cases were reported in Guangdong (Table S1). The outbreak exhibited a two-peak pattern, with the first wave in Foshan primarily concentrated between July 20 to August 16, followed by a larger second wave in the adjacent city of Jiangmen, primarily between September 14 to October 18. Notably, low-level transmission had already begun in Jiangmen during the week of July 20-26, with 44 cases reported before the onset of its major outbreak period, while sporadic cases continued to be reported in Foshan until the week of December 7–13 (Figure 1(a)). Foshan and Jiangmen reported 8,980 and 10,035 cases, with infection attack rates of 19.48 and 25.09 per 10,000 population, respectively (Figure 1(b)). Based on city-level case data, we conducted a space–time analysis using SaTScan that identified five significant clusters: two single-city hotspots (Cluster 2, Foshan, July 20 to August 16, and Cluster 1, Jiangmen, September 14 to October 18), a cluster encompassing five core cities of the Pearl River Delta (Cluster 3), and two smaller secondary clusters (Cluster 4-5) (Figure 1(c); Table S2; Supplemental Methods).

Figure 1.

Spatiotemporal dynamics of the chikungunya outbreak in Guangdong province, China, 2025. a, Weekly reported cases in Guangdong. b, Infection attack rate across cities. Numbers shown next to city name indicate the total reported cases. c, The space-time clusters identified. d, Daily newly reported cases in Foshan. e, Daily newly reported cases in Jiangmen, Xinhui and Pengjiang. In panels d and e, the grey shaded area indicates the period during which a Level – public health emergency response was implemented. Colored dot lines represent fitted curves using an exponential function.

As of August 30, Foshan reported a total of 9,718 cases, with 79.47% in the Shunde district (Table S3). Between September 20 and October 26, Jiangmen reported 8,249 newly confirmed cases, with the Pengjiang and Xinhui districts each accounting for approximately 25% of the total (Table S4). In response to the outbreak, the two cities activated a Level Ⅲ public health emergency response, including nucleic acid testing for chikungunya virus, and comprehensive vector control measures implemented across affected communities [4]. Following these interventions, case numbers declined rapidly in both cities. We fitted an exponential function to the declining phase of daily new cases (Supplemental Methods), with all R² values ≥ 0.79, indicating an acceptable model fit. For Foshan (July 29 to August 30), the estimated exponential decay rate was −0.118 (95% confidence interval [CI]: −0.126 to −0.110), corresponding to a half-life of 5.87 days (95% CI: 5.52–6.28) (Figure 1(d)). For Jiangmen (October 1 to October 25), the decay rate was −0.142 (95% CI: −0.163 to −0.121), with a half-life of 4.88 days (95% CI: 4.25–5.73). At the district level within Jiangmen, Pengjiang had a decay rate of −0.130 (95% CI: −0.158 to −0.102) and a half-life of 5.32 days (95% CI: 4.38–6.79), while Xinhui had a decay rate of −0.147 (95% CI: −0.172 to −0.123) and a half-life of 4.71 days (95% CI: 4.04–5.65).

Discussion

The first imported case of chikungunya in China was reported in 2008 [4]. Since then, sporadic imported and autochthonous cases have been reported in Guangdong, Zhejiang, and Yunnan provinces, with the number of confirmed cases occasionally exceeding 100 [5–7]. However, the 2025 outbreak in Guangdong was unprecedented: even under high-intensity interventions, more than 20,000 cases were reported, highlighting the growing threat posed by mosquito-borne disease. Notably, the two largest clusters were identified in the geographically adjacent cities of Foshan and Jiangmen, but at different stages of the epidemic, suggesting a possible spatial shift in epidemic hotspot over time. The sequential emergence of single-city hotspots, followed by a broader regional cluster later in the epidemic, highlights the marked spatiotemporal heterogeneity of the outbreak. The implemented public health emergence responses, together with other contributing factors such as depletion of the susceptible population and seasonal effects, may have contributed the decline in cases in Foshan and Jiangmen. However, their impacts require further assessment using more detailed modeling analyses [8]. In addition, the decay rates and half-life values were derived from reported confirmed cases and therefore may not fully capture the transmission dynamics of all infections, particularly asymptomatic infections and unreported cases.

Mosquito-borne viruses such as the chikungunya, dengue, and Zika viruses, are transmitted by Aedes mosquitoes and utilize a human-mosquito-human transmission cycle [9]. Climate not only directly influences mosquito development and life cycle [10], but also shapes the spatial distribution of mosquitoes and the viruses that they transmit [11]. With ongoing global warming, the geographical ranges of both mosquitoes and their associated viruses are projected to expand [12]. International travel can facilitate the global spread of mosquito-borne viruses, primarily through infected travelers introducing viruses into areas with native mosquito vectors thereby initiating local transmission at their destinations [13], as observed in this outbreak which was triggered by imported cases. In addition, travel is a major driver of cross-regional transmission of mosquito-borne viruses [14], contributing to the spread of chikungunya cases to other Chinese provinces. Together, global warming, globalization, and human mobility increase the risk of mosquito-borne viruses [10–14]. In response to this, since April 2026 chikungunya fever has been designated as a Class B notifiable infectious disease in China.

Guangdong province, located adjacent to Southeast Asia—a recognized hotspot of mosquito species richness [15]—is particularly vulnerable to the emergence and spread of zoonotic viruses. In addition to effective vector control, early diagnosis of suspected cases, sustained community-based public health education, long-term targeted field surveys, and virome studies of key animals in Southeast Asia countries are urgently needed to assess the prevalence of zoonotic viruses. Mathematical modeling of such surveillance data combined with human mobility patterns between China and Southeast Asia countries can further evaluate the risks of virus importation and local transmission, informing strategies to mitigate and prevent future outbreaks of zoonoses.

Funding Statement

This work was supported by National Key Research and Development Program of China: [Grant Number 2023YFC2307503]; National Natural Science Foundation of China for Distinguished Young Scholars: [Grant Number 32325003]; Shanghai Rising-Star Program: [Grant Number 24YF2732200].

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental Material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/22221751.2026.2695536