Prevalence and trends of syphilis infection among blood donors at a tertiary care centre in South India.

Despite the availability of effective treatment for syphilis for several decades, infection continues to show high prevalence in many developing countries, posing a persistent risk to blood safety. This study aimed to assess syphilis seroprevalence, temporal trends, and the performance of screening assays used for blood donor testing at a tertiary care centre in South India. A total of 28,326 blood donors screened over five years were analysed. From 1 May 2019-31 October 2021, screening was performed using a rapid immunochromatographic test (ICT). Repeat reactive samples were tested by Rapid Plasma Reagin (RPR) and further evaluated using chemiluminescent microparticle immunoassay (CMIA) and Treponema pallidum hemagglutination assay (TPHA). From 1 November 2021-30 April 2024, CMIA replaced ICT as the primary screening assay. True-positive cases were defined as samples reactive on ICT and/or CMIA and confirmed by TPHA; reactive RPR indicated active infection. The overall seroprevalence of syphilis was 0.18%. Among 52 true-positive cases, 53.8% represented active infection and 46.2% inactive infection. An increasing annual trend was observed, with the highest prevalence in 2023. Seropositivity was predominantly seen in males and was more frequent among donors aged 18-30 years. CMIA detected a higher number of true-positive cases than ICT. These findings underscore the need for continuous surveillance, strengthened donor education, and improved awareness of sexually transmitted infections. CMIA demonstrated superior detection and may be preferred as a primary screening assay; however, larger, multicentre studies are required to validate its performance in blood donor screening settings worldwide globally.