Babesia microti in a Canadian blood donor and lookback in a red blood cell recipient

Background and objectives We describe the third documented case of autochthonous human babesiosis in Canada and the second in a Canadian blood donor. Materials and methods Multiple laboratory investigations were carried out on the donor and the immunocompromised recipient of an associated, potentially infectious red blood cell product. Results The donor had not travelled except for outdoor exposure in south-eastern Manitoba, followed by illness and hospital admission. The donor had a notable parasitaemia, positive for Babesia microti using whole blood nucleic acid testing (NAT). The recipient was negative for B. microti by both serology and NAT. Conclusion There was no evidence of transfusion-transmitted babesiosis.