Transfusion-transmitted babesiosis in the era of regional screening: Where are cases still emerging?

To reduce the risk of transfusion-transmitted babesiosis (TTB), the Food and Drug Administration (FDA) released guidance in 2019 requiring Babesia screening of all donations collected in 14 states on the East Coast and Upper Midwest (Connecticut, Delaware, Massachusetts, Maryland, Maine, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Virginia, and Vermont Minnesota and Wisconsin), plus Washington, DC. The American Red Cross (ARC) implemented Babesia blood donation screening in those areas in May 2020. Screening uses a transcription-mediated amplification (TMA) nucleic acid test (NAT) on pools of 16 whole-blood samples. NAT-reactive samples are tested for B. microti antibody by immunofluorescence assay (IFA).

From October 2021 to December 2025, the ARC has identified positive donors in four TTB cases. In all instances, the implicated donation was a Babesia untested red blood cell (RBC) unit collected in a non-endemic state where screening is not performed (West Virginia, Oregon, Georgia, and Michigan). All cases were travel-related: three donors reported travel to endemic states, while the fourth was a resident of an endemic state who donated during a vacation in a non-endemic state.

The regional approach of Babesia blood testing has dramatically reduced the risk of TTB. However, the cases described in this report highlight the ongoing vulnerability posed by donor travel and underscore the need to continue monitoring the current geographic screening strategy.