Translating preventive chemotherapy prevalence thresholds for Schistosoma mansoni from the Kato-Katz technique into the point-of-care circulating cathodic antigen diagnostic test.

• Published in: PLOS Neglected Tropical Diseases
• Main Authors: Oliver Bärenbold, Amadou Garba, Daniel G Colley, Fiona M Fleming, Ayat A Haggag, Reda M R Ramzy, Rufin K Assaré, Edridah M Tukahebwa, Jean B Mbonigaba, Victor Bucumi, Biruck Kebede, Makoy S Yibi, Aboulaye Meité, Jean T Coulibaly, Eliézer K N'Goran, Louis-Albert Tchuem Tchuenté, Pauline Mwinzi, Jürg Utzinger, Penelope Vounatsou
• Format: Article in Journal/Newspaper
• Language: English
• Published: Public Library of Science (PLoS) 2018
• Subjects: Arctic medicine. Tropical medicine; RC955-962; Public aspects of medicine; RA1-1270; Arctic
• Online Access: https://doi.org/10.1371/journal.pntd.0006941; https://doaj.org/article/e31df2bfe9b5436eadff2e32a3f43901

Background Intervention guidelines against Schistosoma mansoni are based on the Kato-Katz technique. However, Kato-Katz thick smears show low sensitivity, especially for light-intensity infections. The point-of-care circulating cathodic antigen (POC-CCA) is a promising rapid diagnostic test detecting antigen output of living worms in urine and results are reported as trace, 1+, 2+, and 3+. The use of POC-CCA for schistosomiasis mapping, control, and surveillance requires translation of the Kato-Katz prevalence thresholds into POC-CCA relative treatment cut-offs. Furthermore, the infection status of egg-negative but antigen-positive individuals and the intensity-dependent sensitivity of POC-CCA should be estimated to determine its suitability for verification of disease elimination efforts. Methodology We used data from settings in Africa and the Americas characterized by a wide range of S. mansoni endemicity. We estimated infection intensity-dependent sensitivity and specificity of each test at the unit of the individual, using a hierarchical Bayesian egg-count model that removes the need to define a 'gold' standard applied to data with multiple Kato-Katz thick smears and POC-CCA urine cassette tests. A simulation study was carried out based on the model estimates to assess the relation of the two diagnostic tests for different endemicity scenarios. Principal findings POC-CCA showed high specificity (> 95%), and high sensitivity (> 95%) for moderate and heavy infection intensities, and moderate sensitivity (> 75%) for light infection intensities, and even for egg-negative but antigen-positive infections. A 10% duplicate slide Kato-Katz thick smear prevalence corresponded to a 15-40% prevalence of ≥ trace-positive POC-CCA, and 10-20% prevalence of ≥ 1+ POC-CCA. The prevalence of ≥ 2+ POC-CCA corresponded directly to single slide Kato-Katz prevalence for all prevalence levels. Conclusions/significance The moderate sensitivity of POC-CCA, even for very light S. mansoni infections where the sensitivity of ...