The timing and location of the first cases of the 1918 influenza pandemic are still controversial, a century after the pandemic became widely recognized. Here, we critically review competing hypotheses on the timing and geographical origin of this important outbreak and provide new historical insights into debates within military circles as to the nature of putative pre-1918 influenza activity. We also synthesize current knowledge about why the 1918 pandemic was so intense in young adults. Although it is still not clear precisely when and where the outbreak began and symptom-based reports are unlikely to reveal the answer, indirect methods including phylogenetics provide important clues, and we consider whether intense influenza activity as far back as 1915 in the USA may have been caused by viral strains closely related to the 1918 one.

中文翻译：

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大流行的起源。

1918年流感大流行的第一批病例的时间和地点仍存在争议，距大流行病被广泛认可已有一个世纪了。在这里，我们批判性地回顾了关于这一重要暴发的时间和地理起源的相互竞争的假设，并为军事圈内关于1918年以前流行流感活动性质的辩论提供了新的历史见解。我们还综合了有关1918年大流行为何在年轻人中如此强烈的最新知识。尽管目前尚不清楚确切的爆发时间和地点，而且基于症状的报道不太可能找到答案，但包括系统发育学在内的间接方法提供了重要的线索，而且我们考虑到早在1915年美国的强烈流感活动是否可能是由与1918年病毒株密切相关的病毒株引起的。