Background

In some tropical countries, such as Brazil, schistosomiasis control programs have led to a significant reduction in the prevalence and parasite burden of endemic populations. In this setting, the Kato-Katz technique, as the standard diagnostic method for the diagnosis of Schistosoma mansoni infections, which involves the analysis of two slides from one fecal sample, loses its sensitivity. As a result, a significant number of infected individuals are not detected. The objective of this study was to perform extensive parasitological testing of up to three fecal samples and include a rapid urine test (POC-CCA) in a moderate prevalence area in Northern Minas Gerais, Brazil, and evaluate the performance of each test separately and in combination.

Methods and findings

A total of 254 individuals were examined with variants of the standard Kato-Katz technique (up to18 Kato-Katz slides prepared from three fecal samples), a modified Helmintex (30 g of feces), the saline gradient (500 mg of feces), and the POC-CCA methods. We established a reference standard taking into consideration all the positive results in any of the parasitological exams. Evaluation of the parasite burden by two Kato-Katz slides confirmed that most of the individuals harbored a light infection. When additional slides and different parasitological methods were included, the estimated prevalence rose 2.3 times, from 20.4% to 45.9%. The best sensitivity was obtained with the Helmintex method (84%). All parasitological methods readily detected a high or moderate intensity of infection; however, all lost their high sensitivity in the case of low or very low intensity infections. The overall sensitivity of POC-CCA (64.9%) was similar to the six Kato-Katz slides from three fecal samples. However, POC-CCA showed low concordance (κ = 0.34) when compared with the reference standard.

Conclusions

The recommended Kato-Katz method largely underestimated the prevalence of S. mansoni infection. Because the best performance was achieved with a modified Helmintex method, this technique might serve as a more precise reference standard. An extended number of Kato-Katz slides in combination with other parasitological methods or with POC-CCA was able to detect more than 80% of egg-positive individuals; however, the rapid urine test (POC-CCA) produced a considerable percentage of false positive results.

中文翻译：

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在寄生虫低负荷流行地区检测肠道血吸虫病的诊断方法的评估：盐梯度，Helmintex，Kato-Katz和快速尿检

背景

在一些热带国家，例如巴西，血吸虫病控制计划已大大减少了地方性人群的患病率和寄生虫负担。在这种情况下，作为诊断曼氏血吸虫感染的标准诊断方法的加藤-卡兹技术，涉及从一个粪便样品中分析两个载玻片，从而失去了灵敏度。结果，未检测到大量感染的个体。这项研究的目的是对多达三个粪便样品进行广泛的寄生虫学测试，并在巴西米纳斯吉拉斯州中度流行地区进行快速尿液测试（POC-CCA），并分别评估每种测试的性能。组合。

方法和发现

使用标准的Kato-Katz技术的变体（从三个粪便样品制备多达18个Kato-Katz载玻片），改良的Helmintex（30 g粪便），盐水梯度（500 mg粪便），和POC-CCA方法。我们建立了参考标准，其中考虑了任何寄生虫学检查中的所有阳性结果。通过两张Kato-Katz载玻片对寄生虫负担的评估证实，大多数人都患有轻度感染。如果再加上其他玻片和不同的寄生虫学方法，估计患病率上升了2.3倍，从20.4％增至45.9％。使用Helmintex方法可获得最佳灵敏度（84％）。所有寄生虫学方法都容易检测出高强度或中等强度的感染。然而，在低强度或极低强度感染的情况下，所有人都失去了高敏感性。POC-CCA的总体敏感性（64.9％）与来自三个粪便样品的六个Kato-Katz载玻片相似。但是，与参考标准相比，POC-CCA显示出较低的一致性（κ= 0.34）。

结论

推荐的Kato-Katz方法大大低估了S的患病率。曼索尼氏菌感染。由于使用改良的Helmintex方法可获得最佳性能，因此该技术可以用作更精确的参考标准。结合其他寄生虫学方法或POC-CCA的大量Kato-Katz玻片能够检测出80％以上的鸡蛋阳性个体。但是，快速尿检（POC-CCA）产生了相当大比例的假阳性结果。