Screening Blood Donations Mitigates Transfusion-Transmitted Babesiosis Risk

Babesia microti bacteria
Babesia microti bacteria
Screening blood donations for Babesia microti in endemic areas eliminates transfusion-transmitted babesiosis effectively.

Screening blood donations for Babesia microti in endemic areas eliminates transfusion-transmitted babesiosis effectively, according to data published in Transfusion.

A total of 506, 540 blood donation samples from Massachusetts, Connecticut, Minnesota, and Wisconsin were screened for B microti by either fluorescence immunoassay or real-time polymerase chain reaction between June 2012 and May 2018. Of these, 1299 samples were reactive: 177 samples were positive for B microti DNA and antibody and 25 were positive only for DNA. During the same period, 23 donations of unscreened samples from Massachusetts and Connecticut were involved in cases of transfusion-transmitted babesiosis. Therefore, the risk for transmitting infection from an unscreened unit in these states was 15.6 times greater (P =.0026) than the risk when receiving a blood transfusion from a screened donation.

Results indicated that the highest number of positive donations occurred in Connecticut and Massachusetts and also revealed that 83% of positive tests across all 4 states were antibody-positive only. Of note, DNA positive samples, which indicate active transmission, also occurred in all 4 states. In Connecticut, where 96% of donations of whole blood are screened for B microti, there have been zero cases reported from donors living in the state since 2016, and positive donor rates have also dropped from 0.67% in 2013 to 0.23% in 2017. Data from ongoing follow-up studies indicate that seroconversion will occur in only 10% of donors who are antibody positive within 1 year, and 94% of those who are positive on polymerase chain reaction testing become negative within a year.

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The study investigators concluded that screening in endemic regions is associated with a significant reduction in transfusion-transmitted babesiosis; however, they noted that whether there is a need to defer donors with an antibody-only positive result is unclear. The researchers recommended challenging the assumption that direct assays such as nucleic acid testing may lack clinical sensitivity and therefore may be replaced with antibody screening. They further recommended that screening with validated and appropriate tests should be considered in all areas that have ongoing risk because of clinical cases of babesiosis and blood donors who are positive for B microti.


Tonnetti L, Townsend RL, Deisting BM, Haynes JM, Dodd RY, Stramer SL. The impact of Babesia microti blood donation screening [published online November 30, 2018]. Transfusion. doi: 10.1111/trf.15043