Evaluation of droplet digital PCR for the clinical diagnosis of toxoplasmosis

The diagnosis of active toxoplasmosis in fetus, newborns, and immunocompromised patients relies on molecular detection of the parasite DNA in various samples according to the clinical setting. The quality of molecular diagnosis is essential to guide specific treatment. Today, real-time PCR (qPCR) based on the REP-529 target is the reference method, but given the emergence of droplet digital PCR (ddPCR) in other diagnostic fields, it is essential to evaluate its clinical performance for the diagnosis of toxoplasmosis. In this study, we evaluated the Naica Crystal ddPCR system (Stilla Technologies) on 64 samples from patients with confirmed toxoplasmosis (30 congenital infection, 23 infections in immunocompromised patients, and 5 ocular toxoplasmosis) and 21 negative samples from patients without toxoplasmosis. Our results showed a concordance of 97% between qPCR and ddPCR, and a good correlation (<i>R</i> ² = 0.80) between the C <i>_T</i> of the qPCR and the concentration in copies/µL obtained in ddPCR. However, we observed a matrix effect leading to a fluctuation of the positive threshold and impacting the separability score. Optimization of the ddPCR program according to the sample type is essential to ensure reliable interpretation.IMPORTANCETo date, droplet digital PCR (ddPCR) contributes to the detection of infectious agents in the environment, but few studies have evaluated its interest in human diagnosis, particularly the Naica Crystal ddPCR. This study shows that it has similar performance to real-time PCR for the diagnosis of toxoplasmosis and could be of interest for parasite quantification, but its cost limits its use.