Possible NAT-negative transfusion-transmitted Babesia microti.

Background: The incidence of transfusion-transmitted babesiosis (TTB) has declined substantially in recent years following the introduction of geographically selective nucleic acid testing (NAT) by blood collectors. This approach has proven quite effective in interdicting parasite-infected units from US regions where Babesia is endemic and is complemented by donor screening questions about prior diagnosis (used in lieu of NAT in non-Babesia-endemic states). Despite these successes, however, breakthrough cases continue to occur due to limitations in the current geographically targeted testing strategy.

Case report: Herein, we report a Minnesota donor reinstated almost 3.5 years after a Babesia NAT-positive donation whose first post-reinstatement donation tested NAT-negative. Three months later, a subsequent donation tested NAT-positive for Babesia microti. Notification of the hospital that transfused the NAT-negative red blood cell unit revealed a likely B. microti transmission.

Discussion: This reverse-notification TTB case was unlikely to have been the result of either a product from an asymptomatic untested donor from a non-endemic state infected during travel to an endemic area or a tick-borne infection of the transfusion recipient. More likely, TTB resulted from transfusion of a NAT-negative unit donated 3 months prior to the involved donor's subsequent NAT-positive collection. To our knowledge, this is the first reported potential Babesia NAT failure.