Transfusion-Associated Babesiosis in the United States: A Description of Cases

Background: Babesiosis is a potentially life-threatening disease caused by intraerythrocytic parasites, which usually are tickborne but also are transmissible by transfusion. Tickborne transmission of Babesia microti mainly occurs in 7 states in the Northeast and the upper Midwest of the United States. No Babesia test for screening blood donors has been licensed. Objective: To ascertain and summarize data on U. S. transfusion-associated Babesia cases identified since the first described case in 1979. Design: Case series. Setting: United States. Patients: Case patients were transfused during 1979-2009 and had posttransfusion Babesia infection diagnosed by 2010, without reported evidence that another transmission route was more likely than transfusion. Implicated donors had laboratory evidence of infection. Potential cases were excluded if all pertinent donors tested negative. Measurements: Distributions of ascertained cases according to Babesia species and period and state of transfusion. Results: 159 transfusion-associated B. microti cases were included; donors were implicated for 136 (86%). The case patients' median age was 65 years (range, <1 to 94 years). Most cases were associated with red blood cell components; 4 were linked to whole blood-derived platelets. Cases occurred in all 4 seasons and in 22 (of 31) years, but 77% (122 cases) occurred during 2000-2009. Cases occurred in 19 states, but 87% (138 cases) were in the 7 main B. microti-endemic states. In addition, 3 B. duncani cases were documented in western states. Limitation: The extent to which cases were not diagnosed, investigated, reported, or ascertained is unknown. Conclusion: Donor-screening strategies that mitigate the risk for transfusion transmission are needed. Babesiosis should be included in the differential diagnosis of unexplained posttransfusion hemolytic anemia or fever, regardless of the season or U. S. region.