(P-TS-111) Transfusion-Transmitted Babesiosis and the Effectiveness of a Regional Testing Approach.

Babesia microti, an intraerythrocytic parasite endemic in northeastern and midwestern states, has been considered the leading case of transfusion-transmitted infection in the US for decades.

Study

Design/Methods: The American Red Cross (ARC) implemented Babesia blood donation screening in May 2020 in 14 states on the East Coast (Northern and Mid-Atlantic, plus Washington DC) and Upper Midwest, as required by the US Food and Drug Administration. Screening uses a transcription-mediated amplification nucleic acid assay (NAT) in pools of 16 whole blood samples. Reactive samples are tested for B. microti antibody (Ab) by immunoglobulin G immunofluorescence (IFA). One follow-up sample is collected from consenting donors at least four weeks after the index donation.

Results/Findings:

From May 2020 to March 2024, the ARC screened over 6.4 million donations and identified 1600 Babesia reactives (0.02%). The number of reactive donations identified during the tick season (May-November) has been increasing from 300 (0.03%) in 2020 to 431 (0.05%) in 2023. Higher rates of reactive donations were collected in the Babesia-endemic states of Connecticut, Massachusetts, Maine, New Hampshire, New Jersey, New York, and Pennsylvania. Follow-up donations were collected from 442 donors, and 378 (85%) remained NAT reactive up to 121 days after index. Ab-positive samples represented 78% of the total NAT-reactive donations. Ab-negative donations (window-period, n=355) corresponded to 22% of the total reactives and were collected mainly between May and July (75%). When followed, 83 of 114 (58%) donors seroconverted.

Since implementing Babesia testing, the ARC has identified positive donors in five transfusion-transmitted-babesiosis (TTB) cases. In all cases, the implicated donation was not tested by NAT for Babesia because it was collected in a state where screening is not required (Ohio, West Virginia, Oregon, Georgia, and Michigan). Two implicated donors lived in states bordering endemic areas but did not have relevant travel histories. The remaining three cases were travel-related: two donors reported travel to endemic states, while the third was a resident of an endemic state who donated during a vacation in a non-endemic state.

Conclusions:

Implementing Babesia testing in endemic areas in the US has demonstrated high effectiveness, with no case of TTB attributed to a tested unit. However, the regional testing approach does not protect from infections acquired during travel or endemic area residents donating in non-endemic states, nor does it account for the geographic expansion of the parasite to areas currently considered non-endemic.