Babesia blood donor screening: A tool for safety and surveillance

BACKGROUND: Babesia is a transfusion-transmissible, tick-borne parasite endemic in the northeastern and upper midwestern US. Since 2020, nucleic acid test screening of blood donations has been implemented in endemic areas to reduce transfusion-transmitted babesiosis. METHODS: American Red Cross blood donations collected between May 2020 and April 2026 in 13 endemic states and Washington, DC, were screened using the FDA-licensed Procleix Babesia transcription-mediated amplification assay. Reactive donations were analyzed by season, geography, donor characteristics, and state-level reactivity rates. Incidence estimates were evaluated using rolling 2-year periods. RESULTS: About 10 million donations were screened, of which 2505 were Babesia-reactive. Overall donor reactivity increased significantly from 0.02% during 2020-2021 to 0.03% during 2021-2026 (p < .001). Significant increases were observed in Maine, New York, and Pennsylvania, and no state demonstrated a significant decline. Donation reactivity exhibited a consistent seasonal pattern, while geographic analyses showed expansion of donor reactivity across the northeastern US, particularly along the eastern seaboard. Incidence increased from 63.2 to 71.0 per 100,000 person-years across the study period, with sustained increases in several states. Among 1638 reinstated donors, 59% returned to donate and 2% tested reactive again, suggesting persistent infection or reinfection. CONCLUSIONS: Six years of routine Babesia screening have effectively protected the blood supply while providing valuable surveillance for asymptomatic infection. Rising donor reactivity, expanding geographic distribution, and evidence of persistent or recurrent infection indicate an increasing risk of babesiosis in the United States and support continued screening and surveillance.