Usefulness of dried blood spot samples for monitoring hepatitis C treatment outcome and reinfection among people who inject drugs in a test-and-treat program.

Dried blood spots (DBS) are a reliable tool to diagnose viremic hepatitis C virus (HCV) infection. We evaluated the clinical performance of a DBS-based molecular assay for the assessment of cure and reinfection after on-site treatment at a harm reduction center (HRC). Genotyping from DBS samples was also assessed to discriminate reinfection from treatment failure. People who inject drugs (PWID) from an ongoing test-and-treat pilot at the largest HRC in Barcelona were included in the study. HCV-RNA detection from DBS collected after treatment (with follow-up at 12, 36, and 60 weeks) was compared with a molecular point-of-care test using finger-stick blood (GeneXpert). Baseline and follow-up DBS samples were genotyped by NS5B sequencing or commercial real-time PCR. Among treated patients, 193 follow-up DBS samples were tested. The DBS-based assay showed 100% specificity (129/129), and sensitivity ranged from 84.4% to 96.1% according to different viral load cut-offs (from detectable to 3000 IU/mL). Sensitivity as test of cure (follow-up 12) ranged from 85.1% to 97.4%. Among the 64 patients with recurrent viremia, 10.9% had low viral loads (≤1000 IU/mL); HCV genotyping allowed us to classify 73.5% of viremic cases either as reinfection or as treatment failure. DBS samples are useful to assess cure and differentiate reinfection from relapse after HCV antiviral treatment in the real world, facilitating decentralization of treatment and posttreatment follow-up in PWID. However, a fraction of patients presented with low viral loads, limiting viremia detection and genotyping in DBS and, therefore, repeat testing is recommended.