Diagnostic accuracy of plasma cell-free DNA qPCR for Schistosoma haematobium assessed by Bayesian latent class analysis in a cohort of pregnant women from Lambaréné, Gabon.

Abstract

Background: Effective diagnosis of Schistosoma haematobium is critical for disease management. However, current tools often lack sensitivity for low-intensity infections, a challenge noted in the recent WHO Roadmap for Neglected Tropical Diseases. This study aimed to evaluate a novel cell-free DNA (cfDNA) quantitative Polymerase Chain Reaction (qPCR) assay, utilizing 20 µl of plasma with crude DNA extraction. This approach intends to improve diagnostic accuracy and lower implementation barriers for molecular tests in field settings. We compared its performance against urine filtration microscopy and the Up-converting Reporter Particle Lateral Flow Circulating Anodic Antigen (UCP-LF CAA) test in pregnant women from Lambaréné, Gabon.

Methods: A prospective cross-sectional study was conducted on 296 pregnant women in Gabon. EDTA blood, urine, and stool samples were collected from December 2018 to November 2020. Urine samples were analyzed by urine filtration microscopy and UCP-LF CAA. The cfDNA qPCR assay was performed retrospectively on 20 µl of frozen plasma using a simplified DNA extraction method. Diagnostic accuracy was assessed via sensitivity, specificity, and agreement measures. Bayesian latent class analysis (BLCA) was used to estimate test performance in the absence of a gold standard.

Results: Diagnostic positivity varied: 24.3% by cfDNA qPCR, 18.6% by urine filtration microscopy, and 20.9% by UCP-LF CAA. Agreement between tests was limited. BLCA indicated qPCR to be the most sensitive (74.0%, 95% CrI: 57.2-90.8), followed by UCP-LF CAA (65.7%, 95% CrI: 49.0-82.8). Microscopy was the most specific (94.9%, 95% CrI : 89.6-99.3). Estimated prevalence ranged between 22.5 and 27.1%. Receiver operating characteristic (ROC) analysis confirmed good individual performance (AUC 0.837-0.868), with performance improving when combining any two tests (AUC up to 0.931).

Conclusions: This study validates the high sensitivity of a novel cfDNA qPCR approach using only 20 µl of plasma, demonstrating performance comparable to microscopy and UCP-LF CAA. While microscopy maintains high specificity, combining it with a high-sensitivity test such as qPCR or UCP-LF CAA provides significant diagnostic improvement. Further optimizing the specificity of this streamlined qPCR assay brings us closer to a highly accurate, feasible point-of-care diagnostic crucial for schistosomiasis control programs in resource-limited settings.