Re-emerging Syphilis Among Blood Donors: Epidemiological Signals, Screening Uncertainties and Implications for Transfusion Safety

Abstract

Syphilis has re-emerged as a major sexually transmitted infection in many regions, and blood services are increasingly detecting reactive and confirmed results among donors. This trend is important for two distinct reasons: it may signal changing infection patterns in populations eligible to donate, and it may alter the residual probability that infectious Treponema pallidum enters the blood supply. These issues are related but not equivalent. This critical narrative review evaluates contemporary donor epidemiology, the biological plausibility of transfusion transmission, the strengths and limitations of current screening algorithms, and the policy consequences of rising seroreactivity. Literature published from 1 January 2000 to 23 May 2026 was selected through live searches of PubMed/MEDLINE, Crossref metadata, DOI records, authoritative institutional sources, and citation networks, with older foundational reports retained where necessary. Recent surveillance from North America, Europe, Latin America, Asia and Africa consistently indicates higher positivity among first-time donors and marked variation by age, sex, geography, migration history and access to care. Yet between-study comparisons are weakened by heterogeneous case definitions, assay combinations, donor populations and denominators. Treponemal screening is highly sensitive but cannot distinguish untreated active infection from previously treated infection, while non-treponemal reactivity is influenced by disease stage, treatment and biological false positivity. Historical transmissions and experimental studies confirm that viable organisms can be present in donated blood, particularly during early infection and in fresh components, but modern processing, storage, donor selection and testing make documented transmission uncommon. Rising donor positivity should therefore be interpreted primarily as an epidemiological and quality-system signal, not as direct evidence of frequent transfusion transmission. Blood services require harmonised definitions of recent infection, transparent confirmatory pathways, donor-centred referral, linked public-health surveillance and resource-sensitive testing policies. Future research should connect serology with treatment history, behavioural data, component fate and recipient outcomes so that safety measures are proportionate to demonstrable risk.