Prevalence of circulating Treponema pallidum DNA and RNA in blood donors with confirmed‐positive syphilis tests

BACKGROUND: Although there have been no well-documented cases of transfusion-transmitted syphilis in more than 30 years, serologic tests for syphilis (STS) continues to be required for donated blood. Previously, the methods for detecting viable spirochetes were dependent on the use of the rabbit infectivity test. DNA PCR and RNA RT-PCR were applied to assess the presence of Treponema pallidum DNA or RNA in blood donors with confirmed-positive results in STS. STUDY DESIGN AND METHODS: This case series describes T. pallidum DNA and RNA testing of platelet concentrates prepared from blood donors with reactive results in an automated treponemal screening test and positive test results in the fluorescent treponomal antibody absorption test. The first DNA test was specific for the T. palladium polA gene. The second DNA test was a multiplex PCR using a T. pallidum 47-kDa gene target. The RT-PCR for RNA used T. pallidum 16S rRNA as a template for production of a cDNA target. RESULTS: One hundred sixty-nine samples (including rapid plasma reagin [RPR]+ and RPR-) tested for T. pallidum DNA and/or RNA were negative. CONCLUSIONS: A lack of demonstrable T. pallidum DNA or RNA suggests that blood donors with confirmed-positive results in STS are unlikely to have circulating T. pallidum in their blood and that that their blood is unlikely to be infectious for syphilis.