Objective To detect global infectious disease events occurring outside China in September 2025 and assess the importation risk to China and international travel risk.

Methods Utilizing open-source intelligence on the Internet, this study conducts event-based surveillance of priority infectious diseases and adopts the risk matrix methodology to build an indicator system by integrating disease-, country- and event-specific indicators in terms of transmission likelihood and severity of consequences in order to assess the risk of the importation and the risk of international travel.

Results In September 2025, 17 infectious diseases were detected to form events or outbreaks in 31 countries worldwide. In terms of importation risk to China, there are 2 high-risk events and 21 medium-risk events; in terms of international travel risk, there are 1 high-risk events and 22 medium-risk events.

Conclusion It is recommended to focus on the potential import risks posed by the dengue fever in Thailand and the chikungunya fever in France. Regarding overseas travel risks, it is advised that travelers abroad pay close attention to the diphtheria in Nigeria. Compared to August, in September, special attention should continue to be paid to the dengue fever in Thailand and the diphtheria in Nigeria. General attention should also be paid to the Ebola hemorrhagic fever in the Democratic Republic of Congo; the dengue fever in Brazil, Panama, and India; the cholera in Haiti; the chikungunya fever in Bangladesh, Macao, China, and Brazil; the polio in Pakistan, Afghanistan and Somalia; the plague in Mongolia and the United States; the West Nile virus disease in Russia, the United States, and Canada; the Zika in Mexico; the Lassa fever in Nigeria; and the Rift Valley fever in Senegal.