Craddock Hannah, Spencer Simon E F, Didelot Xavier
Department of Statistics, University of Warwick, United Kingdom.
Qualcomm Institute, University of California San Diego, San Diego, CA, USA.
Infect Dis Model. 2025 Aug 5;10(4):1418-1432. doi: 10.1016/j.idm.2025.07.017. eCollection 2025 Dec.
The transmission dynamics of an epidemic are rarely homogeneous. Super-spreading events and super-spreading individuals are two types of heterogeneous transmissibility. Inference of super-spreading is commonly carried out on secondary case data, the expected distribution of which is known as the offspring distribution. However, this data is seldom available. Here we introduce a multi-model framework fit to incidence time-series, data that is much more readily available. The framework consists of five discrete-time, stochastic, branching-process models of epidemics spread through a susceptible population. The framework includes a baseline model of homogeneous transmission, a unimodal and a bimodal model for super-spreading events, as well as a unimodal and a bimodal model for super-spreading individuals. Bayesian statistics is used to infer model parameters using Markov Chain Monte-Carlo methods. Model comparison is conducted by computing Bayes factors, with importance sampling used to estimate the marginal likelihood of each model. This estimator is selected for its consistency and lower variance compared to alternatives. Application to simulated data from each model identifies the correct model for the majority of simulations and accurately infers the true parameters, such as the basic reproduction number. We also apply our methods to incidence data from the 2003 SARS outbreak and the Covid-19 pandemic caused by SARS-CoV-2. Model selection consistently identifies the same model and mechanism for a given disease, even when using different time series. Our estimates are consistent with previous studies based on secondary case data. Quantifying the contribution of super-spreading to disease transmission has important implications for infectious disease management and control. Our modelling framework is disease-agnostic and implemented as an R package, with potential to be a valuable tool for public health.
传染病的传播动态很少是均匀的。超级传播事件和超级传播个体是两种异质性传播性类型。超级传播的推断通常基于二代病例数据进行,其预期分布被称为子代分布。然而,这种数据很少可得。在此,我们引入一个适用于发病时间序列的多模型框架,这类数据更容易获取。该框架由五个离散时间、随机、分支过程模型组成,用于描述传染病在易感人群中的传播。该框架包括均匀传播的基线模型、用于超级传播事件的单峰和双峰模型,以及用于超级传播个体的单峰和双峰模型。使用贝叶斯统计方法,通过马尔可夫链蒙特卡罗方法推断模型参数。通过计算贝叶斯因子进行模型比较,使用重要性抽样来估计每个模型的边际似然。选择这个估计器是因为它与其他方法相比具有一致性和更低的方差。将其应用于每个模型的模拟数据,在大多数模拟中都能识别出正确的模型,并准确推断出诸如基本再生数等真实参数。我们还将我们的方法应用于2003年非典疫情和由SARS-CoV-2引起的新冠疫情的发病数据。即使使用不同的时间序列,模型选择对于给定疾病始终能识别出相同的模型和机制。我们的估计与之前基于二代病例数据的研究一致。量化超级传播对疾病传播的贡献对传染病管理和控制具有重要意义。我们的建模框架与疾病无关,并作为一个R包实现,有可能成为公共卫生领域的一个有价值的工具。