Mathematics Institute, University of Warwick, Coventry, CV4 7AL, UK.
London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK.
Philos Trans R Soc Lond B Biol Sci. 2023 Oct 9;378(1887):20220408. doi: 10.1098/rstb.2022.0408. Epub 2023 Aug 21.
Several countries have come close to eliminating leprosy, but leprosy cases continue to be detected at low levels. Due to the long, highly variable delay from infection to detection, the relationship between observed cases and transmission is uncertain. The World Health Organization's new technical guidance provides a path for countries to reach elimination. We use a simple probabilistic model to simulate the stochastic dynamics of detected cases as transmission declines, and evaluate progress through the new public health milestones. In simulations where transmission is halted, 5 years of zero incidence in autochthonous children, combined with 3 years of zero incidence in all ages is a flawed indicator that transmission has halted (54% correctly classified). A further 10 years of only occasional sporadic cases is associated with a high probability of having interrupted transmission (99%). If, however, transmission continues at extremely low levels, it is possible that cases could be misidentified as historic cases from the tail of the incubation period distribution, although misleadingly achieving all three milestones is unlikely (less than 1% probability across a 15-year period of ongoing low-level transmission). These results demonstrate the feasibility and challenges of a phased progression of milestones towards interruption of transmission, allowing assessment of programme status. This article is part of the theme issue 'Challenges and opportunities in the fight against neglected tropical diseases: a decade from the London Declaration on NTDs'.
一些国家已接近于消除麻风病，但仍持续低水平检出麻风病例。由于从感染到检出的潜伏期长且高度可变，观察到的病例与传播之间的关系并不明确。世界卫生组织的新技术指南为各国提供了一条实现消除的路径。我们使用简单的概率模型来模拟随传播下降而出现的检出病例的随机动态，并通过新的公共卫生里程碑来评估进展。在传播停止的模拟中，5 年内本土儿童零发病，加上所有年龄组 3 年内零发病，是一个表明传播已经停止的有缺陷指标（54%的病例正确分类）。再有 10 年仅有偶发散发病例，与传播已中断的可能性很高（99%）相关。然而，如果传播持续处于极低水平，则可能会将病例错误地识别为潜伏期分布尾部的历史病例，尽管不太可能误导性地同时实现所有三个里程碑（在持续低水平传播的 15 年期间，发生概率低于 1%）。这些结果表明，分阶段推进里程碑，以实现传播中断是可行的，但也存在挑战，从而可以评估规划的状况。本文是“在防治被忽视热带病的斗争中面临的挑战和机遇：距离伦敦被忽视热带病宣言十年”主题专辑的一部分。
