例如，在这一突发事件中，人与人之间的传播不能追溯到某一个旅客或单一的社区如学校或工作场所。
For example, in this outbreak, person-to-person transmission cannot be traced back to a traveler, or a single closed community such as a school or workplace.
研究人员下决心要弄清楚禽流感在全球范围内是如何在人与人之间传播的。
Researchers have been determined to figure out how bird flu spreads from human to human worldwide.
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