HTLV Seroprevalence and Associated Factors Among Blood Donors in Shenzhen, China: A Cross-Sectional Study with Longitudinal Follow-Up, 2013–2022

Background: Blood transfusion is a major route of Human T-lymphotropic virus (HTLV) transmission. In this study, we conducted a cross-sectional study of HTLV seroprevalence among blood donors in Shenzhen, with secondary investigations covering signal-to-cutoff (S/CO) predictive value, longitudinal follow-up, epidemiological characteristics, and possible familial clustering. Methods: Retrospective analysis was conducted on 512,200 Shenzhen Blood Center donors (2014–2022, with partial 2013 data). ELISA was utilized for initial HTLV screening, with MP, INNO-LIA and qPCR for confirmation. Confirmed cases received questionnaire follow-up and retesting. Some relatives of confirmed cases also received HTLV-1/2 testing. Results: Among 512,200 donors, 203 were screening-reactive, with 18 confirmed-positive cases (3.51 per 100,000 donors; 95% CI: 2.08–5.55) and 10 indeterminate cases. The screening-reactive rate declined significantly over the decade (p < 0.001), whereas the confirmed-positive rate remained low and showed no significant temporal trend (p = 0.363). Among initially screening-reactive donors, high S/CO values strongly predicted confirmatory positivity, whereas low-level reactivity was mostly transient. Questionnaire data were available for 9 of the 18 confirmed-positive donors (50.0%) and 51 control donors. In this exploratory analysis, only invasive medical procedures occurring in Fujian remained significantly associated with infection (adjusted p = 0.010). Two of the 10 tested family members were confirmed-positive, suggesting possible familial clustering. Conclusions: The confirmed prevalence of HTLV among Shenzhen blood donors was extremely low, and screening reactivity declined significantly over the ten-year period. Screening S/CO values strongly predicted confirmatory results. Fujian-related invasive medical procedures and possible familial clustering are exploratory findings that require confirmation in larger studies. Continued donor screening and blood safety surveillance remain warranted.