Authors

E Kabbas-Piñango³; M Arinaitwe⁴; GJ van Dam²; M Adriko⁴; A Namukuta⁴; A Nankasi⁴; NK Mwima⁴; F Besigye⁴; JM Prada¹; P Lamberton³;  ¹ University of Surrey, UK;  ² Leiden University Medical Center, UK;  ³ School of Biodiversity, One Health and Veterinary Medicine; College of Medical, Veterinary and Life Sciences, University of Glasgow, UK;  ⁴ Vector Borne and Neglected Tropical Diseases Control Division, Ministry of Health, Uganda

Discussion

Over 240 million people are infected with schistosomiasis. Detecting Schistosoma mansoni eggs in stool using Kato–Katz thick smears (Kato-Katzs) is highly specific but lacks sensitivity. The urine-based point-of-care circulating cathodic antigen test (POC-CCA) has higher sensitivity, but issues include specificity, discrepancy between batches and interpretation of trace results. A semi-quantitative G-score and latent class analyses making no assumptions about trace readings have helped address some of these issues. However, intra-sample and inter-sample variation remains unknown for POC-CCAs. We collected 3 days of stool and urine from 349 and 621 participants, from high- and moderate-endemicity areas, respectively. We performed duplicate Kato-Katzs and one POC-CCA per sample. In the high-endemicity community, we also performed three POC-CCA technical replicates on one urine sample per participant. Latent class analysis was performed to estimate the relative contribution of intra- (test technical reproducibility) and inter-sample (day-to-day) variation on sensitivity and specificity. Within-sample variation for Kato-Katzs was higher than between-sample, with the opposite true for POC-CCAs. A single POC-CCA per person with a G3 threshold most accurately assesses individual infections and provides a good prevalence estimate. However, to reach the WHO target product profile requirement of 95% specificity for monitoring and evaluation, at least 2 days of urine sampling, 2 POC-CCAs per person, and the less sensitive threshold of G4 are needed.