Factors associated with active syphilis infection in US blood donors.

Background: Syphilis is increasing globally, with limited monitoring of risk factors in asymptomatic, low-risk populations. Here, we investigate contemporary demographic and behavioral risk factors associated with active syphilis infection (ASI) in US blood donors.

Study design and methods: Beginning with donations in October 2020, four US blood centers implemented standardized risk factor interviews for ASI in blood donors as part of a larger case-control study. Logistic regression models were used to assess ASI associations with demographics and behaviors within 12 months before donation. A conceptual framework explored causal ASI pathways.

Results: Responses were obtained from 369 ASI cases and 868 controls; from all eligible cases, the enrollment rate was 16%. Risk factors in the multivariable-adjusted model included age between 40 and 54 years old (compared to 55+), Black race (compared to White), lower income, single/never married and separated/divorced or widowed status (compared to married or living together), first-time donation, gay/homosexual sexual orientation, having ≥2 male or ≥2 female sexual partners in the 12 months before donation, and a history of sexually transmitted infection. The conceptual risk framework suggests that important determinants of ASI include complex variables and mediators that may have not been fully captured by the questionnaire and regression analyses.

Discussion: Although not fully defining causal relationships with ASI, our findings establish a baseline for factors associated with ASI among US blood donors, which can be used to refine the donor history questionnaire following the implementation of individual risk assessment and further surveillance efforts.