Reverse algorithm for screening of syphilis and trends in prevalence among blood donors in Coastal Karnataka

Transfusion transmissible syphilis is caused by Treponema pallidum; blood donors are traditionally screened with non-treponemal antibody tests to ensure transfusion safety. Detection of specific antibodies against T. pallidum is employed in reverse algorithm screening. We aim to analyze the utility of the reverse algorithm screening strategy for T. pallidum and to determine the prevalence trends among blood donors in our centre.

The study was conducted in a Transfusion Centre catering to the 2030 bedded Tertiary Care Centre in coastal Karnataka in two timelines from 2012 to 2014, and 2019 to 2020, respectively. A fully automated Enzyme-Linked Immunosorbent Assay and Enhanced Chemiluminescence Immunoassay, which detect both IgM and IgG antibodies against T.pallidum were used in the study. Blood donor data from 2008 to 2020 were also analyzed to observe the trend in prevalence rate of syphilis among blood donors.

Among 26329 and 388 blood donors screened with ELISA and ECI, 134 (0.51%) and 9 (2.3%) were reactive to T. pallidum antibodies respectively. TPHA confirmed that 104 and 9 donors were reactive from each of the ELISA and ECI reactive donor groups. The increase in the prevalence of syphilis was observed with the use of reverse algorithm compared to the traditional strategy. The prevalence of syphilis in the present study ranged from 0.02 to 0.28%.

The reverse algorithm screening can give a better result with a positive predictive value of 77.61% and 88.9% for ELISA and ECI. respectively Our study found that the use of reverse algorithm might increase the blood discard rate slightly but adds on to safety of blood components.