Methods: The review epidemiological investigation research in 9 countries 52 villgaes of Panshi, Liaoyuan, Baishan, Jilin province had been done by random chester sampling.

• 方法：用分层随机整群抽样方法对吉林省磐石、辽源、白山3市9个乡、52个村进行回顾性流行病学调查研究。