1Francis I. Proctor Foundation, UCSF, San Francisco, California.
2Department of Epidemiology and Biostatistics, UCSF, San Francisco, California.
Am J Trop Med Hyg. 2020 Jul;103(1):287-294. doi: 10.4269/ajtmh.19-0758. Epub 2020 May 21.
Elimination of an infectious disease requires subcritical transmission, or a reproductive number less than one, and can be assessed with cross-sectional surveys conducted by neglected tropical disease programs. Here, we assess the distribution of onchocerciasis prevalence taken from surveys across sub-Saharan Africa before the initiation of ivermectin in mass drug administrations. Pre-intervention nodular palpation cross-sectional surveys were available from 15 countries in the Expanded Special Project for Elimination of Neglected Tropical Diseases (ESPEN) database. We determined whether the distribution of the prevalence over communities in an area was consistent with a geometric distribution, which previous studies have suggested indicates a subcritical disease. If not, we fitted a negative binominal distribution (hypothetically supercritical) or a mixture of two distributions: geometric (hypothetically subcritical) and Poisson (hypothetically supercritical). The overall distribution of community-level onchocerciasis prevalence estimates from the ESPEN dataset from 2005 to 2014 was not consistent with a geometric distribution. By contrast, data from several countries and parts of countries were consistent with the geometric distribution, for example, some areas within Nigeria and Angola. Even if the geometric distribution suggested pre-intervention subcriticality in more localized geographical areas, our model using pooled survey data of all geographic areas suggests that the entire pre-intervention prevalence does not fit a geometric distribution. Further work will be required to confirm the significance of a geometric distribution for onchocerciasis.
消除传染病需要亚临界传播，即繁殖数小于 1，并且可以通过被忽视的热带病规划进行的横断面调查来评估。在这里，我们评估了在大规模药物管理开始使用伊维菌素之前，在撒哈拉以南非洲进行的横断面调查中获得的盘尾丝虫病流行率的分布情况。在 ESPEN 数据库中，我们从 15 个国家获得了干预前结节触诊横断面调查。我们确定了在一个地区的社区中流行率的分布是否与几何分布一致，这是之前的研究表明指示亚临界疾病的分布。如果不是，我们拟合了负二项分布（假设超临界）或两种分布的混合物：几何分布（假设亚临界）和泊松分布（假设超临界）。2005 年至 2014 年 ESPEN 数据集的社区层面盘尾丝虫病流行率估计的总体分布与几何分布不一致。相比之下，来自几个国家和国家部分地区的数据与几何分布一致，例如尼日利亚和安哥拉的一些地区。即使几何分布表明在更局部的地理区域存在干预前的亚临界性，我们使用所有地理区域的汇总调查数据的模型表明，整个干预前的流行率不符合几何分布。需要进一步的工作来确认几何分布对盘尾丝虫病的意义。
