Concordance of the point-of-care circulating cathodic antigen test for the diagnosis of intestinal schistosomiasis in a low endemicity area

Abstract

Background The Kato-Katz technique is recommended worldwide for the diagnosis of intestinal schistosomiasis, detecting parasite eggs in feces of infected people. However, new tests have been developed in order to facilitate diagnosis, e.g. by detection of specific antigens secreted by schistosomes, such as the circulating cathodic antigen (CCA). The aim of this study was to evaluate the performance of the point-of-care circulating cathodic antigen test (POC-CCA) compared to the Kato-Katz technique in a low prevalence area in the Amazon Region, located in the municipality of Primavera, State of Pará, Brazil. Methods Positivity rates of the POC-CCA test and the Kato-Katz technique were calculated. The sensitivity, specificity, accuracy and kappa coefficient were determined by comparing both methods. The reference standard was established using 16 Kato-Katz slides, 12 of the first fecal sample, two of the second and two of the third one. The study also included the concordance between POC-CCA results and different numbers and combinations of Kato-Katz slides. Results The prevalence of schistosomiasis according to the reference standard or POC-CCA test reached a rate of 9.4% or 23.9%, respectively, among a total of 372 participants. The positivity rates by the Kato-Katz technique increased from 2.4 to 9.4%, according to the increase in the number of slides examined and fecal samples collected. A sensitivity of 55.6%, specificity 76.9%, accuracy 76% and κ coefficient of 0.06 was observed by comparing one slide of the first sample and POC-CCA. Comparing 6 slides from three different samples, two slides of each, with POC-CCA resulted in a sensitivity of 58.3%, specificity 78.4%, accuracy 77% and κ coefficient of 0.16. Finally, the comparison of 16 slides from three different samples with POC-CCA revealed a sensitivity of 65.7%, specificity 80.4%, accuracy 79%, and κ coefficient of 0.27. Conclusions The immunochromatographic test has the potential to be an important tool to combat schistosomiasis because of its practicality and applicability but should be applied with caution in low prevalence areas and in programs that aim to eliminate this disease. Trial registration CAAE#21824513.9.0000.5091 . January 31st, 2014. Electronic supplementary material The online version of this article (10.1186/s40249-019-0551-7) contains supplementary material, which is available to authorized users.

The use of the circulating cathodic antigen (CCA) urine cassette assay for the diagnosis and assessment of cure of Schistosoma mansoni infections in an endemic area of the Amazon region

“…This value yielded a better detection rate than 16 KK slides from three different stool samples, which identified 31 positives (Figure 1). This is a higher rate than that reported by Sousa et al (2019) 21 .…”

“…Currently, the POC-CCA test demonstrated better results than two KK slides 20 . In a study conducted by Sousa et al (2019) 21 in a low prevalence area with low individual parasite loads, it was noticed that the POC-CCA test had similar rates of detection of infected individuals when compared with 9 slides from a single stool sample or 6 slides from 3 different samples. However, the increase in sensitivity had shown an improvement of performance of the POC-CCA test with an increase in the amount of feces analyzed.…”

“…Over the last 30 years, efforts made by the Brazilian Schistosomiasis Control Program have contributed to decreasing the positivity rate and individual parasite loads in endemic areas, consequently hampering S. mansoni egg detection by the KK method 4,9 . The use of two slides under these circumstances does not provide satisfactory diagnostic performance to proceed toward elimination of schistosomiasis as a public health problem 8,[11][12][13][14]21 .…”

“…In the present study, an average of five filters was examined per sample. Eggs were identified correctly following the proposed criteria based on egg elements such as shape, presence of spike, approximated size, well-defined shell, space between the miracidium and shell, and purple color of the miracidium 21 .…”

“…According to data presented in the manufacturer’s manual of the POC-CCA test, the sensitivity rate may vary from 70% to 100%, depending on the intensity of infection 19 . When the POC-CCA test was compared with the KK method, it was reported that a single urine test showed a sensitivity equivalent to that of six 20 or nine KK slides 21 . However, recent studies on the performance of POC-CCA also showed controversial results, with reduced accuracy and elevated false negative or false positive rates, particularly in low prevalence areas 22 , 14 , 17 , 18 .…”