Syphilis testing in blood donors, France, 2007 to 2022

Background: Syphilis in blood donors (BD) has increased in many countries. Aim: We aimed to describe trends in syphilis seroposivity in BD in France, to identify risk factors and assess if a non-treponemic test (NTT) could define BD having recovered from syphilis for more than 1 year. Methods: The analysis covered the period 2007 to 2022 and 45,875,939 donations. Of the 474 BD syphilis-positive in 2022, 429 underwent additional investigations with an NTT. History of syphilis was obtained at the post-donation interview or based on serology results for repeat donors. Results: Until 2021, positivity rates remained stable (mean: 1.18/10,000 donations, range: 1.01-1.38). An increased rate was observed in 2022 (1.74/10,000; p = 0.02). Over the whole study period, prevalence was 2.2 times higher in male than in female BD (4.1 times higher in 2022). The proportion of males with an identified risk factor who have sex with men increased from 16.7% in 2007 to 64.9% in 2022. Based on NTT, 79 (18%) of the donors who were seropositive in 2022 were classified as having been infected in the previous year. History of syphilis was available for 30 of them. All had an infection within the previous 3 years. Among seven donors with a syphilis < 12 months before testing, one had an NTT titre >= 8, three a titre between 1 and 4, three were negative. Conclusion: Syphilis seropositivity increased considerably in BDs in 2022, mostly in males, notably MSM. Available data did not allow appropriate evaluation of the NTT to distinguish recent from past infection.