Evaluation and optimization of the Circulating Cathodic Antigen (CCA) cassette test for Schistosoma mansoni, in rural areas of Tanzania
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 (CCA) cassette test for Schistosoma mansoni in three rural districts of Mwanza region, Tanzania.
Our study was conducted among 404 school-age children (aged 9-12 years) across four different schools, adjacent to Lake Victoria in Tanzania. Stool and urine samples were collected for three consecutive days. For S. mansoni diagnosis, stool samples were examined for eggs with duplicate Kato-Katz, whereas urine samples were tested for presence of antigen by CCA cassettes. The proportion of positive individuals for S. mansoni by three CCA cassettes was higher (75.0%; 303) than for six Kato-Katz (42.6 %; 172). The ‘gold standard’ was built considering the combined results obtained for six Kato-Katz smears and three CCA cassettes from three consecutive days. For CCA cassette performance, three CCA cassettes were more sensitive (94.7%) than six Kato-Katz (53.7%).
In terms of optimization of the CCA cassette test, a Software tool (Image Studio Lite®) has been able to detect the result band in all positive CCA cassettes and pixel quantification has been performed, showing a positive correlation between pixels and CCA cassette intensities and between pixels and egg counts.
In addition, comparison of two different urine concentrations was conducted among 106 school-age children across two different schools in the same area of Mwanza. Collection of urine samples took place in the morning before drinking 0.5 L of water (concentrated-urine) and after (diluted-urine), at the same day and each tested with a single CCA cassette. A total of 84.9% (90) did not show changes in result scores from concentrated to diluted urine, compared to 15.1% (16) that changed result in CCA cassette from concentrated to diluted urine. That indicates that no big changes are occurring between urine groups and therefore the urine collection time has no significant impact on the results of our study.
In conclusion, CCA cassette test seems to be a more appropriate tool for S. mansoni diagnosis compared to Kato-Katz in endemic communities such as Mwanza region. Optimization of the tool in terms of cassette-reading could be assessed by computer software which quantifies the cassette colour band. In terms of urine collection, collection time of the urine is not important for the results of our study.