Flow-S enables field-based detection of low-intensity Schistosoma infections for monitoring and evaluation of control programs

Introduction Schistosomiasis remains a major public health challenge, particularly in sub-Saharan Africa. Detecting low-intensity infections is difficult because conventional parasitological methods lack sufficient sensitivity. Circulating anodic antigen (CAA), a genus-specific biomarker released by Schistosoma worms, enables detection of active Schistosoma infections. However, existing CAA assays require laboratory-based sample processing. We evaluated Flow-S, a field-deployable device for high-sensitivity quantitative CAA detection directly from large-volume, untreated urine samples. Flow-S integrates CAA concentration and quantitative upconverting reporter particle lateral flow (UCP-LF) detection with a portable standalone battery-powered reader for field-use. Methods A prospective study was conducted by local healthcare staff in a remote Schistosoma haematobium -endemic low-to-moderate infection setting. Fresh urine samples (n = 158) from women of reproductive age were analyzed using Flow-S. Paired urine, serum, and stool samples were examined by urine filtration microscopy, Kato-Katz (to exclude S. mansoni ), and laboratory-based UCP-LF CAA reference assays (serum SCAA20 and urine UCAA hT 417). A composite reference standard (CRS) classified individuals as infected when eggs or either reference CAA assay was positive. Flow-S performance was evaluated against the CRS and further assessed using latent class analysis (LCA). Results Complete datasets were available for 115 samples. Flow-S achieved an area under the receiver operating characteristic (ROC) curve of 0.92 and detected all egg-positive infections. Using a positivity threshold of 1.10 pg/mL, Flow-S achieved 80.8% sensitivity and 96.6% specificity, meeting the World Health Organization ideal target product profile requirements for monitoring and evaluation of schistosomiasis control programs. Latent class analysis provided complementary model-based evidence consistent with the high discriminatory performance of Flow-S observed using the composite reference standard. Conclusions Flow-S enables quantitative, field-deployable detection of S. haematobium infections directly from untreated large-volume urine without laboratory pre-treatment. Its high analytical sensitivity and diagnostic performance support its potential for detecting low-intensity infections. At an operational threshold of 1.10 pg/mL, Flow-S met the WHO TPP ideal targets for monitoring and evaluation and showed potential for cost-effective surveillance strategies, including pooled-sample screening for schistosomiasis control and elimination programs.