Nishiura Hiroshi, Cook Alex R, Cowling Benjamin J
PRESTO, Japan Science and Technology Agency, Saitama 332-0012, Japan.
Interdiscip Perspect Infect Dis. 2011;2011:194507. doi: 10.1155/2011/194507. Epub 2010 Dec 23.
Unlike local transmission of pandemic influenza A (H1N1-2009), which was frequently driven by school children, most cases identified in long-distance intranational and international travelers have been adults. The present study examines the relationship between the probability of temporary extinction and the age-dependent next-generation matrix, focusing on the impact of assortativity. Preferred mixing captures as a good approximation the assortativity of a heterogeneously mixing population. We show that the contribution of a nonmaintenance host (i.e., a host type which cannot sustain transmission on its own) to the risk of a major epidemic is greatly diminished as mixing patterns become more assortative, and in such a scenario, a higher proportion of non-maintenance hosts among index cases elevates the probability of extinction. Despite the presence of various other epidemiological factors that undoubtedly influenced the delay between first importations and the subsequent epidemic, these results suggest that the dominance of adults among imported cases represents one of the possible factors explaining the delays in geographic spread observed during the recent pandemic.
与2009年甲型H1N1大流行性流感的本地传播情况不同（后者常由学龄儿童推动传播），在长途国内和国际旅行者中发现的大多数病例都是成年人。本研究考察了暂时灭绝概率与年龄依赖性下一代矩阵之间的关系，重点关注配对性的影响。偏好性混合作为一种良好的近似，捕捉了异质性混合人群的配对性。我们表明，随着混合模式变得更具配对性，非维持性宿主（即自身无法维持传播的宿主类型）对重大疫情风险的贡献会大幅降低，在这种情况下，指示病例中非维持性宿主的比例越高，灭绝的概率就越高。尽管存在各种其他无疑影响了首次输入病例与后续疫情之间延迟的流行病学因素，但这些结果表明，输入病例中成年人占主导地位是解释近期大流行期间观察到的地理传播延迟的可能因素之一。
