Evaluation and optimization of the Circulating Cathodic Antigen (POC-CCA) cassette test for detecting Schistosoma mansoni infection by using image analysis in school children in Mwanza Region, Tanzania

Miriam Casacuberta,Safari Kinunghi,Birgitte J Vennervald,Annette Olsen

doi:10.1016/j.parepi.2016.04.002

Miriam Casacuberta, Safari Kinunghi + Show 2 more

Open Access

https://doi.org/10.1016/j.parepi.2016.04.002

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Abstract

There is a need for diagnostic techniques which are sensitive, specific, rapid and easy to perform at the point-of-care. The aim of this study was to evaluate the diagnostic performance of the Circulating Cathodic Antigen (POC-CCA) assay for Schistosoma mansoni in four schools along the coast of Lake Victoria in Mwanza Region, Tanzania, and to optimize the reading of the POC-CCA test lines by using a computer software image analysis. Initially, a pilot study in 106 school children indicated that time of urine collection did not have an impact on CCA results as 84.9% (90) had identical scores from a urine collected in the morning and a urine taken at midday after drinking 0.5L of water. The main study was conducted among 404 school children (aged 9–12years) where stool and urine samples were collected for three consecutive days. For S. mansoni diagnosis, stool samples were examined for eggs with duplicate Kato-Katz smears, whereas urine samples were tested for presence of antigen by POC-CCA. The proportion of positive individuals for S. mansoni by one POC-CCA was higher compared to two Kato-Katz smears (66.1% vs. 28.7%; p<0.0001). Both proportions increased expectedly when three POC-CCAs were compared to six Kato-Katz smears (75.0% vs. 42.6%; p<0.0001). Three POC-CCAs were more sensitive (94.7%) than six Kato-Katz smears (53.8%) using the combined results of three POC-CCAs and six Kato-Katz smears as the ‘gold standard’. To optimize the reading of the POC-CCA, a Software tool (Image Studio Lite®) was used to read and quantify the colour (expressed as pixels) of the test line on all positive tests, showing a positive correlation between number of pixels and the visually scored intensities and between number of pixels and egg counts. In conclusion, the POC-CCA assay seems to be a more appropriate tool for S. mansoni diagnosis compared to the Kato-Katz method in endemic communities such as Mwanza Region. Optimization of the tool in terms of cassette-reading could be assessed by computer software which was able to quantify the colour of the lines in the strip of the cassette.

Highlights

If the two diagnostic methods were compared for the first stool sample only, the proportion of positive individuals using one performance of the Circulating Cathodic Antigen (POC-Cathodic Antigen (CCA)) was significantly higher compared to two Kato-Katz smears (66.1% vs. 28.7%; χ2 (1) = 111.7, p b 0.0001)
The number of S. mansoni infected children determined by POC-CCA assay of one urine on three consecutive days was significantly higher (p b 0.0005) than the number determined by duplicate Kato-Katz thick smears of one stool sample on the same three days, which is in agreement with previous studies (Erko et al, 2013; Coulibaly et al, 2013; Colley et al, 2013; Mwinzi et al, 2015)
It is in accordance with a recent systematic review which found that below 50% prevalence by Kato-Katz, the prevalence by the POC-CCA assay was between 1.5- and 6-fold higher than prevalence by Kato-Katz, while the two methods yielded approximately the same prevalence when prevalence was above 50% by Kato-Katz (Kittur et al, 2016)

Summary

Introduction

The World Health Organization (WHO) recommends detection of eggs in stool by the Kato-Katz technique (Katz et al, 1972) as the standard tool for the qualitative and quantitative diagnosis of Schistosoma mansoni infection It is the most direct and specific technique by which the presence of a schistosome infection can be established (Hamilton et al, 1998) and has been chosen due to its assumed high specificity of 100% (Doenhoff et al, 2004; Gray et al, 2011), relative simple performance under field conditions and in places with limited health facilities, such as in Sub-Saharan Africa, as well as low cost compared to currently available diagnostic tests (Kongs et al, 2001; WHO, 2002). It has been widely recognized that the Kato-Katz method lacks sensitivity (Ruiz-Tiben et al, 1979; Gryseels and de Vlas, 1996) especially in situations where light intensity is common (Berhe et al, 2004) These light infections are missed and become a potential source of S. mansoni transmission (Erko et al, 2013). Well-trained laboratory technicians are needed in order to perform the test correctly

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