Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, Glasgow, G61 1QH, UK.
Epidemics. 2009 Dec;1(4):221-9. doi: 10.1016/j.epidem.2009.10.002. Epub 2009 Oct 27.
When a few individuals generate disproportionately many secondary cases, targeted interventions can theoretically lead to highly efficient control of the spread of infection. Practical exploitation of heterogeneous transmission requires the sources of variability to be quantified, yet it is unusual to have empirical data of sufficient resolution to distinguish their effects. Here, we exploit extensive data on pathogen shedding densities and the distribution of cases, collected from the same population within the same spatio-temporal window, to expose the comparative epidemiology of independent Escherichia coli O157 strains. For this zoonotic pathogen, which exhibits high-density shedding (supershedding) and heterogeneous transmission in its cattle reservoir, whether targeting supershedding could be an effective control depends critically on the proposed link between shedding density and transmissibility. We substantiate this link by showing that our supershedder strain has nearly triple the R(0) of our non-supershedder strain. We show that observed transmission heterogeneities are strongly driven by superspreading in addition to supershedding, but that for the supershedder strain, the dominant strain in our study population, there remains sufficient heterogeneity in contribution to R(0) from different shedding densities to allow exploitation for control. However, in the presence of substantial within-host variability, our results indicate that rather than seek out supershedders themselves, the most effective controls would directly target the phenomenon of pathogen supershedding with the aim of interrupting or preventing high shedding densities. In this system, multiple sources of heterogeneity have masked the role of shedding densities-our potential targets for control. This analysis demonstrates the critical importance of disentangling the effects of multiple sources of heterogeneity when designing targeted interventions.
当少数个体产生不成比例的大量继发病例时，有针对性的干预措施理论上可以高效控制感染的传播。实际利用异质性传播需要量化变异的来源，但通常没有足够分辨率的经验数据来区分它们的影响。在这里，我们利用从同一时空窗口内同一人群中收集的病原体脱落密度和病例分布的广泛数据，揭示独立的大肠杆菌 O157 菌株的比较流行病学。对于这种具有高密度脱落（超级脱落）和其牛储层中异质性传播的人畜共患病原体，针对超级脱落是否可以作为有效控制措施，关键取决于提出的脱落密度与传染性之间的联系。我们通过表明我们的超级脱落菌株的 R(0)几乎是我们非超级脱落菌株的三倍，证实了这一联系。我们表明，除了超级脱落之外，观察到的传播异质性主要是由超级传播驱动的，但对于我们研究人群中的优势菌株——超级脱落菌株，不同脱落密度对 R(0)的贡献仍存在足够的异质性，允许利用其进行控制。然而，在存在大量宿主内变异性的情况下，我们的结果表明，最有效的控制措施不是直接针对超级脱落者本身，而是直接针对病原体超级脱落现象，旨在中断或防止高脱落密度。在这个系统中，多种异质性来源掩盖了脱落密度的作用——我们控制的潜在目标。这项分析表明，在设计有针对性的干预措施时，必须将多种异质性来源的影响分开来考虑。
