Análise e comparação da sensibilidade e especificidade entre diferentes métodos de diagnóstico para Schistosoma mansoni: gradiente salino, Helmintex®, centrífugo-sedimentação, kato-katz e teste rápido urina (POC-CCA)

Abstract

Human intestinal schistosomiasis, caused by the trematode Schistosoma mansoni, is a neglected tropical disease that affects millions of people in Africa and Latin America. For diagnosis, the World Health Organization (WHO) recommends the Kato-Katz method (KK) with two slides prepared from a single fecal sample as standard coprological method. However, in areas of low endemicity or in subjects with low parasite load, the KK method has shown low sensitivity. As a result, a large number of individuals are diagnosed as false negative, difficulting the control or eradication of the disease. Thus, the objective of this study was to compare the sensitivity and specificity of KK method, Centrifugal-Sedimentation (MIFC), Saline gradient (GRAD), Helmintex (HTX) and Rapid Urine test (POC-CCA) in relation to the Gold Standard, which includes all positive individuals detected by some kind of direct parasitological method. Three fecal samples from 257 individuals, residents of Brejo do Amparo, county of Januária, Minas Gerais, Brazil, were collected during three consecutive days and analyzed by different diagnostic methods. For KK, 14 slides were prepared from the first and two slides from the second and third sample fecal sample. For the saline gradient, 500 mg of feces were used from the first sample. In the case of HTX, we used a total of 30 g of feces from the first sample, which was submitted to filtration and washing procedures, before mixing it with paramagnetic beads. During the preparation of MIFC, 2 g of feces of each sample was homogenized and pooled in preservative solution. The pooled samples were mixed with ethyl ether and then centrifuged. As for the POC-CCA, patients provided a urine sample. The statistical analysis determined the performance of each method in terms of prevalence and sensitivity, and in combination with any other test and also in relation to the parasite burden. The prevalence increased from 20.4% (WHO standard) to 45.9% in the gold standard. The MIFC was the least sensitive method for the diagnosis of schistosomiasis, even in individuals with a high parasite load. The sensitivity of GRAD was equal to that observed with two Kato-Katz slides. In addition, the HTX method showed the best performance, most probably because of the analyzed fecal volume and the successive sample purification processes. An increased number of slides and samples resulted in a better performance of the KK method. However, further reading of more than six slides did not result in a better performance of the method. The POC-CCA presented a performance equal to that of KK with three samples and two slides each, including the detection of individuals with low worm burden. For the combination of different diagnostic methods, the best performance was achieved with the HTX and KK with two slides each from three samples or between HTX and POC-CCA, which showed similar performance. For KK the best combinations were obtained when using six slides from one or three fecal samples with POC-CCA. We conclude that the sensitivity of KK rises with increasing number of slides and / or samples and that a combination of different methods also contributes to a more accurate diagnosis of schistosomiasis in areas of low parasite load. However, this study recommends the use of a combination of the KK method with six slides of the same sample and POC-CCA due to their wider applicability, since it is inexpensive, easy to perform and requires reduced sampling efforts.