Risk profiling of soil-transmitted helminth infection and estimated number of infected people in South Asia: A systematic review and Bayesian geostatistical Analysis

BackgroundIn South Asia, hundreds of millions of people are infected with soil-transmitted helminths (Ascaris lumbricoides, hookworm, and Trichuris trichiura). However, high-resolution risk profiles and the estimated number of people infected have yet to be determined. In turn, such information will assist control programs to identify priority areas for allocation of scarce resource for the control of soil-transmitted helminth infection.MethodologyWe pursued a systematic review to identify prevalence surveys pertaining to soil-transmitted helminth infections in four mainland countries (i.e., Bangladesh, India, Nepal, and Pakistan) of South Asia. PubMed and ISI Web of Science were searched from inception to April 25, 2019, without restriction of language, study design, and survey date. We utilized Bayesian geostatistical models to identify environmental and socioeconomic predictors, and to estimate infection risk at high spatial resolution across the study region.Principal findingsA total of 536, 490, and 410 georeferenced surveys were identified for A. lumbricoides, hookworm, and T. trichiura, respectively. We estimate that 361 million people (95% Bayesian credible interval (BCI) 331–395 million), approximately one-quarter of the South Asia population, was infected with at least one soil-transmitted helminth species in 2015. A. lumbricoides was the predominant species. Moderate to high prevalence (>20%) of any soil-transmitted helminth infection was predicted in the northeastern part and some northern areas of the study region, as well as the southern coastal areas of India. The annual treatment needs for the school-age population requiring preventive chemotherapy was estimated at 165 million doses (95% BCI: 146–185 million).Conclusions/significanceOur risk maps provide an overview of the geographic distribution of soil-transmitted helminth infection in four mainland countries of South Asia and highlight the need for up-to-date surveys to accurately evaluate the disease burden in the region.

研究背景：在南亚地区，数亿人口感染了土源性蠕虫（soil-transmitted helminths），包括似蚓蛔线虫（Ascaris lumbricoides）、钩虫（hookworm）以及毛首鞭形线虫（Trichuris trichiura）。然而，该地区高精度的感染风险分布图谱以及准确的感染人数估算结果尚未明确。此类信息将助力土源性蠕虫感染防控项目确定优先防控区域，合理调配稀缺防控资源。

研究方法：本研究通过系统综述，筛选了南亚四个内陆国家（孟加拉国、印度、尼泊尔及巴基斯坦）内有关土源性蠕虫感染的现况调查研究。检索范围涵盖PubMed及ISI Web of Science数据库自建库起至2019年4月25日的所有相关文献，未对语言、研究设计及调查时间设置限制。本研究采用贝叶斯地统计模型（Bayesian geostatistical models），识别影响感染风险的环境与社会经济预测因子，并在研究区域内以高空间分辨率估算感染风险。

主要研究结果：针对似蚓蛔线虫、钩虫及毛首鞭形线虫，本研究分别筛选得到536项、490项及410项带地理坐标的调查研究。经估算，2015年南亚地区至少感染一种土源性蠕虫的人口达3.61亿（95%贝叶斯可信区间（Bayesian credible interval, BCI）：3.31亿~3.95亿），约占南亚总人口的四分之一。其中似蚓蛔线虫为最主要的感染虫种。研究区域东北部、部分北部区域以及印度南部沿海地区的任意土源性蠕虫感染率均达到中至高感染水平（>20%）。需开展预防性化疗的学龄人口年度治疗剂量需求经估算为1.65亿剂（95% BCI：1.46亿~1.85亿剂）。

结论与意义：本研究生成的风险图谱全面呈现了南亚四个内陆国家土源性蠕虫感染的地理分布特征，并强调亟需开展最新调查以精准评估该地区的疾病负担。