Fogarty International Center, National Institute of Health, Bethesda, MD, United States; Ecology and Evolutionary Biology Department, University of California, Los Angeles, United States; F.I. Proctor Foundation, University of California, San Francisco, United States.
Epidemics. 2013 Sep;5(3):131-45. doi: 10.1016/j.epidem.2013.05.002. Epub 2013 Jun 3.
Many diseases exhibit subcritical transmission (i.e. 0<R0<1) so that infections occur as self-limited 'stuttering chains'. Given an ensemble of stuttering chains, information about the number of cases in each chain can be used to infer R0, which is of crucial importance for monitoring the risk that a disease will emerge to establish endemic circulation. However, the challenge of imperfect case detection has led authors to adopt a variety of work-around measures when inferring R0, such as discarding data on isolated cases or aggregating intermediate-sized chains together. Each of these methods has the potential to introduce bias, but a quantitative comparison of these approaches has not been reported. By adapting a model based on a negative binomial offspring distribution that permits a variable degree of transmission heterogeneity, we present a unified analysis of existing R0 estimation methods. Simulation studies show that the degree of transmission heterogeneity, when improperly modeled, can significantly impact the bias of R0 estimation methods designed for imperfect observation. These studies also highlight the importance of isolated cases in assessing whether an estimation technique is consistent with observed data. Analysis of data from measles outbreaks shows that likelihood scores are highest for models that allow a flexible degree of transmission heterogeneity. Aggregating intermediate sized chains often has similar performance to analyzing a complete chain size distribution. However, truncating isolated cases is beneficial only when surveillance systems clearly favor full observation of large chains but not small chains. Meanwhile, if data on the type and proportion of cases that are unobserved were known, we demonstrate that maximum likelihood inference of R0 could be adjusted accordingly. This motivates the need for future empirical and theoretical work to quantify observation error and incorporate relevant mechanisms into stuttering chain models used to estimate transmission parameters.
许多疾病表现出亚临界传播(即 0<R0<1),因此感染会以自我限制的“口吃链”形式发生。给定一组口吃链,每条链中病例数量的信息可用于推断 R0,这对于监测疾病出现并建立地方性传播的风险至关重要。然而,由于不完善的病例检测,作者在推断 R0 时采用了各种替代措施,例如丢弃孤立病例的数据或合并中等大小的链。这些方法中的每一种都有可能引入偏差,但尚未报道对这些方法的定量比较。通过采用基于负二项式后代分布的模型,该模型允许传播异质性的程度可变,我们对现有的 R0 估计方法进行了统一分析。模拟研究表明,当传播异质性被不正确建模时,它会显著影响针对不完善观察设计的 R0 估计方法的偏差。这些研究还强调了孤立病例在评估估计技术是否与观察数据一致方面的重要性。对麻疹暴发数据的分析表明,允许灵活传播异质性程度的模型具有最高的似然得分。合并中等大小的链通常与分析完整的链大小分布具有相似的性能。然而,只有当监测系统明显有利于全面观察大链而不是小链时,截断孤立病例才是有益的。同时,如果知道未知病例的类型和比例的数据,我们证明可以相应地调整 R0 的最大似然推断。这促使我们需要进行未来的实证和理论工作,以量化观察误差,并将相关机制纳入用于估计传播参数的口吃链模型中。