As of Friday afternoon, all the 37 patients have been found in five localities of Zhongshan City since July 16, and it is likely that more cases will be reported, provincial health authorities said.
The patients have been hospitalised, showing mild symptoms of muscle pains and skin rashes, said He Jianfeng, a health expert related to disease control and prevention centre.
None of them had undertaken trip to Southeast Asia, where most infections occur, indicating that the outbreak was not imported, He said, while attributing the outbreak to the rainy weather which favoured mosquito reproduction.
The number of contractions of the potentially fatal mosquito-borne disease has been rising year on year. Experts have warned about controlling and preventing the mosquito that transmit it.