Cycling profiles of unconfirmed syphilis repeat-reactive serology results during influenza and COVID-19 vaccination campaigns: September 2017-January 2022

ABSTRACT

Background: All donations at Canadian Blood Services (CBS) are screened for syphilis using a serology screening and confirmation test algorithm. Currently, syphilis repeat-reactive (RR) results lead to the indefinite deferral of CBS donors regardless of supplementary test results. We have previously described a temporal association of RR results with seasonal public health influenza vaccination campaigns that generally start in September and continue through winter. As of December 2020, there has also been an intensive COVID-19 public health vaccination campaign in Canada. Aims: To track temporal associations between RR, unconfirmed syphilis results among CBS blood donors and Canadian influenza and COVID-19 vaccination campaigns. Methods: All donations were tested on the PK 7300 instrument (Beckman Coulter;Brea, CA, USA) with the PK TP system test kit. Confirmatory laboratory testing was undertaken at reference laboratories using the Treponema pallidum particle agglutination (TP-PA) test. Syphilis RR results that did not confirm were obtained for CBS donations between September 2017 to January 2022. Data on donor influenza and COVID-19 vaccination histories, within 3 months of donation, were extracted. The temporal periodicity of unconfirmed syphilis RR results was graphed against vaccination data. Respiratory virus data were acquired from the Public Health Agency of Canada Respiratory Virus Detection Surveillance System. Results: Periodicity of RR, unconfirmed syphilis rates September 2017-January 2022. Summary/Conclusions: We have previously noted a cyclical temporal trend in the number of RR, unconfirmed syphilis specimens with peaks corresponding to influenza vaccine campaigns or widespread community circulation of respiratory viruses. Although insufficient to establish a causal association, this analysis suggests that incidence of RR, unconfirmed syphilis results in Canadian blood donors may be variably influenced at different times of year by one or more of at least three factors (1) influenza vaccination campaigns, (2) the COVID-19 vaccination campaign, and (3) circulation of respiratory viruses in the presence or absence of circulating seasonal influenza. Moreover, other mechanisms may affect these trends. For example, syphilis assays such as the PK TP test kit that detect IgM may be prone to false positive results that do not confirm either after influenza vaccine, COVID- 19 vaccination or during a respiratory virus season. (Table Presented).