Study of diagnostic accuracy of Helmintex, Kato-Katz, and POC-CCA methods for diagnosing intestinal schistosomiasis in Candeal, a low intensity transmission area in northeastern Brazil

Abstract

Control initiatives have successfully reduced the prevalence and intensity of schistosomiasis transmission in several localities around the world. However, individuals that release low numbers of eggs in their feces may not be detected by classical methods that are limited by low sensitivity. Given that accurate estimates of prevalence are key to implementing planning control actions for the elimination of schistosomiasis, new diagnostic tools are needed to effectively monitor infections and confirm transmission interruption. The World Health Organization recommends the Kato-Katz (KK) thick smear as a parasitological test for epidemiological surveys, even though this method has been demonstrated to underestimate prevalence when egg burdens are low. The point-of-care immunodiagnostic for detecting schistosome cathodic circulating antigen (POC-CCA) method has been proposed as a more sensitive substitute for KK in prevalence estimations. An alternative diagnostic, the Helmintex (HTX) method, isolates eggs from fecal samples with the use of paramagnetic particles in a magnetic field. Here, a population-based study involving 461 individuals from Candeal, Sergipe State, Brazil, was conducted to evaluate these three methods comparatively by latent class analysis (LCA). The prevalence of schistosomiasis mansoni was determined to be 71% with POC-CCA, 40.% with HTX and 11% with KK. Most of the egg burdens of the individuals tested (70%) were < 1 epg, thereby revealing a dissociation between prevalence and intensity in this locality. Therefore, the present results confirm that the HTX method is a highly sensitive egg detection procedure and support its use as a reference method for diagnosing intestinal schistosomiasis and for comparative evaluation of other tests.

Diagnosis of Schistosoma mansoni infections: what are the choices in Brazilian low-endemic areas?

“… 18 , 32 Several studies have investigated the effect of modifications to the K-K protocol, such as collecting stool samples on different days, increasing sample size and the number of slides analysed, and the addition of other parasitological methods in low-endemic areas. 18 , 31 , 32 , 33 , 36 , 60 , 61 …”

“…These techniques have exhibited high sensitivity, however, their reduced specificity in comparison to microscopy-based methods make them inadequate as single-use tests. 33 , 36 Because of the high specificity of egg-based techniques for detecting active infections, new sensitive parasitological methods have been developed, including the saline gradient (SG) 37 and Helmintex (HX). 38 Improvements have also been made to the conventional protocol of K-K, and these include increasing the number of samples and the number of slides to be evaluated.…”

“… 46 Only 10 studies were conducted in Brazil, which has a significantly different prevalence and morbidity profile, and these tests yielded controversial results regarding sensitivity and specificity. 25 , 26 , 33 , 36 , 39 , 47 , 48 , 49 , 50 , 51 …”

Response to Argemi et al. 2019

“…It is indicated that a double count was performed, but it is not clear if two stool samples were analyzed or if two slides of a single stool sample were analyzed. It is noteworthy that the diagnosis of schistosomiasis is difficult due to the variable kinetics of egg elimination in stool (Berhe et al, 2004;Lindholz et al, 2018). The only way to ensure the reliability of this technique is by repeatedly assessing stool samples.…”

Schistosomiasis: from established diagnostic assays to emerging micro/nanotechnology-based rapid field testing for clinical management and epidemiology

“…Such parasitological detection (PD) is widely used because it is relatively efficacious and moderately cost-effective for case management, screening or surveillance. The success of control measures against schistosomiasis has been difficult to determine because the sensitivity of PD decreases when there is no egg excretion, or it diminishes, principally in areas of low endemicity [25] Other direct parasitological tests for intestinal schistosomiasis are the Kato-Katz (KK) [33] technique, the miracidia hatching test (MHT) [34], the salinity gradient [35] and on the recently developed FLOTAC [36][37][38][39][40][41] and Helmintex assay [42][43][44][45][46][47]. The KK technique has the advantage of egg quantification in fresh stool samples.…”