Confirmatory testing of military blood donors screening positive for Babesia infection

BACKGROUND: Babesia microti is a transfusion-transmitted pathogen. The US Food and Drug Administration (FDA) recommends blood donor screening only in endemic states, whereas the Military Health System performs universal Babesia screening regardless of geographic location. However, the epidemiology of Babesia positivity and clinical follow-up among blood donors in non-endemic regions remains poorly characterized.

STUDY DESIGN AND METHODS: We conducted a retrospective study evaluating Babesia screening results from three military blood donation centers in non-endemic states: Naval Base San Diego, Wright-Patterson Air Force Base, and Joint Base San Antonio-Lackland. All donations collected between January 1, 2021 and December 31, 2025 underwent nucleic acid testing using the Procleix Babesia Assay. Positive donors underwent retrospective chart review to assess demographics, confirmatory testing, clinical follow-up, and treatment outcomes.

RESULTS: Among 97,861 donations screened, eight donors tested positive for Babesia (8.17 per 100,000 donations). San Diego demonstrated the highest positivity rate (11.53 per 100,000), followed by Wright-Patterson (8.55 per 100,000) and San Antonio (5.82 per 100,000). Five donors were active-duty military personnel with medical records available for review, and three underwent follow-up clinical evaluation. Follow-up approaches varied considerably and include empiric treatment without confirmatory testing, antibody testing, peripheral blood smear evaluation, and polymerase chain reaction (PCR) testing. All clinically evaluated donors were asymptomatic, and there were no documented complications related to babesiosis.

DISCUSSION: Babesia positivity among military blood donors in non-endemic regions was rare. Variation in diagnostic evaluation and clinical management highlights the need for standardized follow-up protocols for military donors with positive screening results.