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Blood Center/Blood Hospital-Based Donor Center

(P-BB-50) Increased Unconfirmed Peak Syphilis Repeat Reactive Rates in Canadian Blood Doors in the COVID-19 Pandemic Period Compared to the Pre-pandemic Period.

Saturday, October 14, 2023
Background/Case Studies: An anti-treponemal-specific IgM/IgG test is used to screen blood donations for syphilis. Previously, we identified a temporal association between unconfirmed syphilis repeat-reactive (RR) results and other potential confounders: vaccination campaigns for influenza/COVID-19, community-circulating influenza virus (I), COVID-19, and other respiratory viruses (ORV) typically overlapping with influenza (IORV). In this study we assessed the unconfirmed peak syphilis RR rates in the COVID-19 pandemic period compared to the pre-pandemic period.

Study

Design/Methods: Influenza and COVID-19 vaccination histories in the preceding 3 months were extracted. Aggregated syphilis RR results that did not confirm were collated (September 2017-December 2022; PK 7300 instrument [Beckman Coulter; Brea, CA, USA]). Peak syphilis RR results were compared against; influenza/COVID-19 vaccination data. IORV and Respiratory Syncytial Virus (RSV) data was acquired from the Public Health Agency of Canada Respiratory Virus Detection Surveillance System. Data analysis used GraphPad Prism 9.5.0 (GraphPad Software, Boston, MA, USA).

Results/Findings: Results and findings are listed in the Table.

Conclusions: Multiple immune pressures in the post-pandemic period are associated with a noticeable increase in syphilis RR rates in the pandemic period compared to the pre-pandemic period. We speculate that re-emerging immune pressures from vaccination and/or community-acquired COVID-19 or IORV (including RSV) are generating non-specific immune responses identified by the IgM component of the syphilis test.

Importance of research: Syphilis assays that detect IgM are potentially prone to false-positives due to non-specific immune activation in blood donors. Here we note an increase in unconfirmed syphilis repeat reactive rates in the period following the emergence of COVID-19. Understanding trends in unconfirmed repeat reactive rates of syphilis may allow blood operators to plan for pressures on donor re-entry programs.