标题： 在存在宿主传播或输入病例的情况下估计繁殖数的一些简单规则 显示英文标题

标题： Some simple rules for estimating reproduction numbers in the presence of reservoir exposure or imported cases

摘要： 基本繁殖数（$R_0$）是隔离种群中疾病消亡或存活的阈值参数。 然而，没有人种群是完全与其他人类或动物种群隔离的。 我们使用分 compartment 模型来推导出具有局部人际传播和来自其他来源暴露的人口的基本繁殖数的简单规则： either 是一个水库暴露或输入病例。 我们引入了由水库驱动或输入驱动的疾病的概念：在没有水库暴露或输入病例的情况下，这种疾病会在感兴趣的人口中消亡（因为$R_0<1$），但可能仍然具有足够的传播性，使得许多或大多数感染是从该人口中的感染者获得的。 我们表明，在最简单的情况下，$R_0<1$当且仅当从外部来源获得的感染比例超过疾病患病率，并探讨人口异质性和多种菌株的相互作用如何影响这一规则。 我们在两个关于艰难梭菌感染和定植的案例研究中应用这些规则：医院环境中考虑输入病例的艰难梭菌，以及一般人群中考虑动物水库暴露的艰难梭菌。 我们证明，即使是在医院适应的、高度传播的 NAP1/RT027 菌株，在一项对住院患者的标志性研究中其繁殖数也小于 1，因此是由进入研究医院的定植和感染患者维持的。 我们认为，如果仅将 13.0% 的传播归因于动物水库，那么应将艰难梭菌视为由水库驱动的疾病。 显示英文摘要

摘要： The basic reproduction number ($R_0$) 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 for populations with local person-to-person transmission 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 $R_0<1$), 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, $R_0<1$ 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 cases 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.