Though imported dengue fever infections have initiated local outbreaks in China, the scale and risk of onward transmission differ significantly across provinces, according to a study published recently in China CDC Weekly.

The study analyzed national surveillance data from 2005 to 2025, covering 148,893 reported cases. Indigenous infections accounted for 134,129 cases, or 90.1 percent, and imported cases made up 14,764 cases, or 9.9 percent.

Researchers found that imported cases tended to rise in May and June ahead of the domestic epidemic season in late summer and autumn, suggesting they played an early role in seeding local transmission.

Most imported cases were linked to Southeast Asian countries. The sources diversified over time, expanding from nine countries or regions in 2005 to 52 by 2025. The source with the highest number of cases shifted from Cambodia in 2015–2019 to Myanmar in 2020–2025.

The study identified Yunnan and Guangdong as persistent high-risk areas for local spread following imported infections. Yunnan's imported cases were mainly associated with Myanmar, while Guangdong reported more diverse sources, including Cambodia, Thailand, and Malaysia. Hunan and Chongqing have also shown rising risks in recent years, while Sichuan and Jiangsu have remained relatively lower-risk.

Imported cases were mainly men aged 25 to 49, with farmers, workers, and commercial or service-sector employees among the most affected groups.

Indigenous cases showed a more balanced sex ratio, with household, unemployed, and retired people forming the largest occupational group.

The findings suggest China's dengue control strategy should integrate source interception of imported cases with tailored interventions addressing distinct importation profiles, evolving local transmission risks, and population characteristics across provinces.