McLure Angus, Glass Kathryn
Research School of Population Health, Australian National University, 62 Mills Rd, Acton, 0200, ACT, Australia.
Research School of Population Health, Australian National University, 62 Mills Rd, Acton, 0200, ACT, Australia.
Theor Popul Biol. 2020 Aug;134:182-194. doi: 10.1016/j.tpb.2020.04.002. Epub 2020 Apr 15.
For many diseases, the basic reproduction number (R) is a threshold parameter for disease extinction or survival in isolated populations. However no human population is fully isolated from other human or animal populations. We use compartmental models to derive simple rules for the basic reproduction number in populations where an endemic disease is sustained by a combination of local transmission within the population and exposure from some other source: either a reservoir exposure or imported cases. We introduce the idea of a reservoir-driven or importation-driven disease: diseases that would become extinct in the population of interest without reservoir exposure or imported cases (since R<1), but nevertheless may be sufficiently transmissible that many or most infections are acquired from humans in that population. We show that in the simplest case, R<1 if and only if the proportion of infections acquired from the external source exceeds the disease prevalence and explore how population heterogeneity and the interactions of multiple strains affect this rule. We apply these rules in two case studies of Clostridium difficile infection and colonisation: C. difficile in the hospital setting accounting for imported cases, and C. difficile in the general human population accounting for exposure to animal reservoirs. We demonstrate that even the hospital-adapted, highly-transmissible NAP1/RT027 strain of C. difficile had a reproduction number <1 in a landmark study of hospitalised patients and therefore was sustained by colonised and infected admissions to the study hospital. We argue that C. difficile should be considered reservoir-driven if as little as 13.0% of transmission can be attributed to animal reservoirs.
对于许多疾病而言，基本再生数（R）是孤立人群中疾病灭绝或存续的一个阈值参数。然而，没有任何人类群体能完全与其他人类或动物群体隔离开来。我们使用 compartmental 模型来推导基本再生数在人群中的简单规则，在这些人群中，一种地方病由人群内部的局部传播以及来自其他某种来源的暴露共同维持：要么是来自储存宿主的暴露，要么是输入病例。我们引入了储存宿主驱动或输入驱动疾病的概念：在没有储存宿主暴露或输入病例的情况下（因为R<1），这些疾病在目标人群中会灭绝，但它们的传播性可能仍足以使许多或大多数感染源自该人群中的人类。我们表明，在最简单的情况下，当且仅当从外部来源获得的感染比例超过疾病患病率时，R<1，并探讨人群异质性和多种菌株的相互作用如何影响这一规则。我们将这些规则应用于艰难梭菌感染和定植的两个案例研究中：医院环境中的艰难梭菌（考虑输入病例），以及普通人群中的艰难梭菌（考虑接触动物储存宿主）。我们证明，即使是医院适应性强、传播性高的艰难梭菌NAP1/RT027菌株，在一项针对住院患者的标志性研究中其再生数也<1，因此是由入住该研究医院的定植和感染患者维持的。我们认为，如果仅13.0%的传播可归因于动物储存宿主，那么艰难梭菌应被视为储存宿主驱动的疾病。
