<scp>HTLV</scp> screening and confirmatory testing among blood donors in São Paulo: A cross‐sectional study

INTRODUCTION: Human T-cell lymphotropic virus types 1 and 2 (HTLV-1/2) are transfusion-transmissible retroviruses associated with severe diseases, and blood donor screening is mandatory in Brazil. Increasing HTLV-related discard rates at our institution prompted this study to determine the prevalence and incidence of HTLV-1/2 and to investigate the presence of HTLV-3 among donations reactive in the ARCHITECT rHTLV-I/II CMIA assay. METHODS: A retrospective cross-sectional study was conducted among 220 340 volunteer blood donors at Fundação Pró-Sangue/Hemocentro de São Paulo, Brazil, between September 2019 and July 2021. Real-time PCR assays for HTLV-1/2 and HTLV-3 were performed. INNO-LIA HTLV-I/II was used as the confirmatory test for samples reactive in screening with the ARCHITECT rHTLV-I/II CMIA assay. RESULTS: Among 220 340 donations, 404 (0.18%) were initially reactive by CMIA, and 223 (0.10%) were further analysed. Of these, 59 (26.5%) were confirmed HTLV-1/2 positive by INNO-LIA, and 42 (18.8%) were indeterminate. Annual rates of initially reactive donations were 0.20% (2019), 0.20% (2020), and 0.15% (2021). Overall HTLV prevalence was 0.027%, and incidence was 1.36 per 100 000 donations. Real-time PCR detected HTLV DNA in 54 (24.2%) samples; no HTLV-3 cases were identified. An S/CO cutoff ≥4.0 increased the positive predictive value from 47.6% to 66.1%. CONCLUSION: These findings highlight the epidemiological and diagnostic challenges of HTLV-1/2 in blood donors. Reliance solely on serological screening thresholds is limited, reinforcing the essential role of confirmatory molecular and serological testing to ensure accurate diagnosis and strengthen blood safety in Brazil.