Comparison of individual and pooled diagnostic examination strategies during the national mapping of soil-transmitted helminths and Schistosoma mansoni in Ethiopia

BackgroundLaboratory-based studies have highlighted that pooling stool and urine samples can reduce costs and diagnostic burden without a negative impact on the ability to estimate the intensity of soil-transmitted helminth (STH, Ascaris lumbricoides, Trichuris trichiura and hookworms) and schistosome infections (Schistosoma mansoni and S. haematobium). In this study, we compare individual and pooled stool examination strategies in a programmatic setting.MethodsStool samples were collected from 2,650 children in 53 primary schools in Amhara Regional State, Ethiopia, during the national mapping of STHs and schistosome infections. Eggs of STHs and S. mansoni were quantified in both individual and pooled samples (pools were made from 10 individual samples) using a single Kato-Katz smear.Principal findingsA pooled diagnostic examination strategy provided comparable estimates of infection intensity with higher fecal egg count (expressed in eggs per gram of stool (EPG)) than those based on individual strategy (Ascaris: 45.1 EPG vs. 93.9, p = 0.03; Trichuris: 1.8 EPG vs. 2.1 EPG, p = 0.95; hookworms: 17.5 EPG vs. 28.5 EPG, p = 0.18; S. mansoni: 1.6 EPG vs. 3.4 EPG, p = 0.02), but had lower sensitivity (Ascaris: 90.0% vs. 55.0%; Trichuris: 91.7% vs. 16.7%; hookworms: 92.6% vs. 61.8%; S. mansoni: 100% vs. 51.7%, p Conclusions/SignificanceA pooled approach holds promise for the rapid assessment of intensity of helminth infections in a programmatic setting, but it is not major cost-saving strategy. Further investigation is required to determine when and how pooling can be utilized. Such work should also include validation of statistical methods to estimate prevalence based on pooling samples. Finally, the comparison of operational costs across different scenarios of national program management will help determine whether pooling is indeed worthwhile considering.

背景 基于实验室的研究表明，混合粪便与尿液样本可在不影响土源性蠕虫（soil-transmitted helminth, STH，即似蚓蛔线虫（Ascaris lumbricoides）、毛首鞭形线虫（Trichuris trichiura）和钩虫）以及血吸虫（曼氏血吸虫Schistosoma mansoni和埃及血吸虫S. haematobium）感染强度估算准确性的前提下，降低检测成本与诊断负担。本研究在项目实施场景中，对比了单个粪便样本检测与混合样本检测策略。
方法 在埃塞俄比亚阿姆哈拉州53所小学的2650名儿童中采集粪便样本，该采样工作依托土源性蠕虫与血吸虫感染国家制图项目开展。采用单张Kato-Katz涂片法（Kato-Katz smear），对单个样本以及混合样本（每10个个体样本组成1组混合样本）中的土源性蠕虫与曼氏血吸虫虫卵进行定量检测。
主要结果 混合检测策略可获得与单个样本检测相当的感染强度估算结果，但其粪便虫卵计数（以每克粪便虫卵数即eggs per gram of stool, EPG表示）更高：似蚓蛔线虫：93.9 EPG vs 45.1 EPG，p=0.03；毛首鞭形线虫：2.1 EPG vs 1.8 EPG，p=0.95；钩虫：28.5 EPG vs 17.5 EPG，p=0.18；曼氏血吸虫：3.4 EPG vs 1.6 EPG，p=0.02。但混合检测的灵敏度更低：似蚓蛔线虫：55.0% vs 90.0%；毛首鞭形线虫：16.7% vs 91.7%；钩虫：61.8% vs 92.6%；曼氏血吸虫：51.7% vs 100%，p<0.001（原文此处疑似存在格式遗漏）。
结论与意义 混合检测策略有望在项目实施场景中快速评估蠕虫感染强度，但并非大幅节约成本的方案。仍需进一步研究以明确混合样本检测的适用时机与具体方式，此类研究还应验证基于混合样本的感染率估算统计方法。最后，对比国家项目管理不同场景下的运营成本，将有助于明确混合检测策略是否确实具有应用价值。