2021 FDA Science Forum
Effect of Storage on Treponema Pallidum Infectivity in Whole Blood and Platelets
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Contributing OfficeCenter for Biologics Evaluation and Research
Abstract
Background
Universal testing of blood donations for evidence of syphilis has been in place since 1938. Testing and other factors contributed to the disappearance of transfusion-transmitted syphilis (TTS) including routine refrigeration of blood and components. Cold temperatures are thought to inactivate Treponema pallidum, the spirochete bacterium causing syphilis, rapidly. Hence, some in the blood industry have concluded that syphilis testing adds no safety benefit and have suggested that FDA drop it.
Purpose
The goal of the project is to reassess whether routine storage of blood and platelets reliably eliminates the risk of TTS. The results of this study will inform FDA decision whether to consider discontinuing the requirement of universal testing of donor blood for syphilis.
Methodology
We conducted studies mimicking three FDA-approved storage conditions of whole blood and platelets. We spiked fresh human whole blood with treponemes and stored them at 1-6 °C for 9 days. We also spiked fresh human platelets with treponemes and stored them at either room temperature (20-24 °C) or at 1-6 °C for 7 and 14 days respectively. We sampled aliquots at various times after spiking and injected into rabbit testes, a gold standard model for detecting syphilis infectivity. Control rabbits were inoculated with either uninfected blood samples or inactivated treponemes. We assayed rabbit sera for seroconversion using a commercial treponemal antibody test (TP-PA, Fujirebio) and a non-treponemal (ASI RPR Card Test, Arlington Scientific) and monitored animals for development of overt orchitis. All studies were terminated after 90 or 120 days.
Results
Rabbits developed orchitis or their sera tested positive by serology after injection of treponeme-spiked blood and platelets stored up to 7 days. We observed no differences in survival of T. pallidum in blood that was stored cold or at room temperature. No rabbits in the negative control group developed orchitis or syphilis antibodies.
Conclusions
Treponemes in banked donor blood can survive for at least 7 days. The findings support continued universal syphilis testing of all donations to ensure blood safety.
