科学家们正逐步确认能综合起来引发疑难病症的各种因素。当卡特琳娜飓风在2005年8月引发湾区海滨的塌陷时,它之所以能够造成如此严重而持久的破坏,是因为几大因素的完美结合:不完善的基础设施、通讯设备陈旧,以及急救系统的瘫痪。这些因素综合起来造成了美国近年来最严重的灾难。类似地,许多顽疾也是各种因素综合作用的结果。如果把这些因素独立 Scientists are gradually identifying the various factors that can combine to trigger a difficult illness. When Hurricane Katrina triggered the collapse of the waterfront in the Bay Area in August 2005, it caused so grave and long-lasting damage because of the perfect combination of imperfect infrastructure, obsolete communications equipment and First aid system paralyzed. Together, these factors have caused the worst disaster in the United States in recent years. Similarly, many illnesses are also the result of a combination of factors. If these factors are independent