EVERY summer at the height of the rainy season, villagers in a corner of southwestern China would suddenly die of cardiac arrest.

No one knew what caused Yunnan Sudden Death Syndrome, blamed for an estimated 400 deaths in the past three decades.

Now, after a five-year investigation, an elite unit from China's Center for Disease Control and Prevention believes it has pinpointed the cause: an innocuous-looking small mushroom known as Little White.

The search began in 2005 and took investigators to remote villages spread over the rural highlands of Yunnan Province, said Robert Fontaine, an epidemiologist with the US Centers for Disease Control and Prevention.

There was "this very obvious clustering of deaths in villages in very short periods of time in the summer," said Fontaine, who helped in the investigation.

By 2008, investigators had discovered a relatively unknown mushroom in a number of homes where people had died.

The mushroom is not usually sold in the markets, because it's too small.

A public information campaign to warn against eating the mushrooms dramatically reduced the number of deaths. However, the mystery has not yet been definitively solved.

Testing found the mushroom contained some toxins, but not enough to be deadly. Chinese scientists need to isolate the toxin and test whether it triggers cardiac arrests.

Researchers have hypothesized that there is a second agent. "There is a lot of work left to do," Fontaine said. "We really need additional lab investigations."

• height [hait] n.高度；顶点；卓越 (初中英语单词)
• arrest [ə´rest] vt.逮捕 n.逮捕；停止 (初中英语单词)
• investigation [in,vesti´geiʃən] n.调查(研究) (初中英语单词)
• remote [ri´məut] a.遥远的；偏僻的 (初中英语单词)
• province [´prɔvins] n.省；领域；范围 (初中英语单词)
• obvious [´ɔbviəs] a.明显的；显而易见的 (初中英语单词)
• mystery [´mistəri] n.神秘；秘密；故弄玄虚 (初中英语单词)
• deadly [´dedli] a.致命的 ad.死一般地 (初中英语单词)
• additional [ə´diʃənəl] a.附加的，额外的 (初中英语单词)
• mushroom [´mʌʃru:m] n.蘑菇 vi.采蘑菇 (高中英语单词)
• relatively [´relətivli] ad.比较地；相对地 (高中英语单词)
• campaign [kæm´pein] n.战役；行动 vi.从军 (高中英语单词)
• isolate [´aisəleit] vt.隔离；孤立 (高中英语单词)
• prevention [pri´venʃən] n.预防；阻止；妨碍 (英语四级单词)
• southwestern [,sauθ´westən] a.西南的 (英语六级单词)