一、导言由于不断地认识到环境及生活方式对人类健康的影响,因此,人们已越来越重视对可能引起疾病的各种因子的研究。尽管其中许多致病因子的研究可在实验室内进行,但要确定人类是否真正会受到危害,主要还有待于流行病学调查。当因、果联系较强,特别是当因作用后不久即有果出现,则这种因果联系很易发现。实验或临床观察往往能足以提示职业的危险性,但只有用流行病学调查才能确定危险性的存在 I. INTRODUCTION With the ongoing recognition of the environmental and lifestyle implications of human health, there has been a growing emphasis on research into the various factors that may cause illness. Although many of these virulence factors can be studied in the laboratory, determining whether humankind is truly harmful or not is largely beyond the epidemiological investigation. When the cause and effect are strong, especially when the fruit appears soon after its action, this causal link is easy to find. Experimental or clinical observations are often enough to indicate occupational risk, but only epidemiological surveys can determine the presence of risk