MRC Tropical Epidemiology Group, Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom.
Vector Biology Department, Liverpool School of Tropical Medicine, Liverpool, United Kingdom.
PLoS Negl Trop Dis. 2020 Sep 3;14(9):e0008576. doi: 10.1371/journal.pntd.0008576. eCollection 2020 Sep.
The ability of cluster-randomized trials to capture mass or indirect effects is one reason for their increasing use to test interventions against vector-borne diseases such as malaria and dengue. For the same reason, however, the independence of clusters may be compromised if the distances between clusters is too small to ensure independence. In other words they may be subject to spillover effects.
We distinguish two types of spatial spillover effect: between-cluster dependence in outcomes, or spillover dependence; and modification of the intervention effect according to distance to the intervention arm, or spillover indirect effect. We estimate these effects in trial of insecticide-treated materials against the dengue mosquito vector, Aedes aegypti, in Venezuela, the endpoint being the Breteau index. We use a novel random effects Poisson spatial regression model. Spillover dependence is incorporated via an orthogonalized intrinsic conditional autoregression (ICAR) model. Spillover indirect effects are incorporated via the number of locations within a certain radius, set at 200m, that are in the intervention arm.
From the model with ICAR spatial dependence, and the degree of surroundedness, the intervention effect is estimated as 0.74-favouring the intervention-with a 95% credible interval of 0.34 to 1.69. The point estimates are stronger with increasing surroundedness within intervention locations.
In this trial there is some evidence of a spillover indirect effect of the intervention, with the Breteau index tending to be lower in locations which are more surrounded by locations in the intervention arm.
集群随机试验能够捕捉到总体或间接效应，这是它们越来越多地被用于测试针对疟疾和登革热等虫媒疾病的干预措施的原因之一。然而，出于同样的原因，如果集群之间的距离太小，无法确保独立性，那么集群的独立性可能会受到影响。换句话说，它们可能会受到溢出效应的影响。
我们区分了两种类型的空间溢出效应：结果之间的集群间依赖性，或溢出依赖性；以及根据与干预臂的距离来改变干预效果，或溢出间接效应。我们在委内瑞拉针对登革热蚊子媒介 Aedes aegypti 的杀虫剂处理材料试验中估计了这些效应，终点是布雷托指数。我们使用了一种新颖的随机效应泊松空间回归模型。通过正交化内在条件自回归（ICAR）模型来纳入溢出依赖性。通过在 200m 半径内处于干预臂的位置数量来纳入溢出间接效应。
从具有 ICAR 空间依赖性和包围程度的模型中，干预效果估计为 0.74-有利于干预-95%可信区间为 0.34 至 1.69。随着干预位置内的包围程度增加，点估计值更强。
在这项试验中，干预的间接溢出效应有一些证据，布雷托指数在更受干预臂位置包围的位置上趋于更低。
