Transfusion-Transmitted Babesia microti Risks Transfusion-Transmitted Babesia microti Identified Through Hemovigilance

Background: Babesia microti, a tick-borne parasite endemic to the northeast and upper Midwest, is the primary cause of human babesiosis in the United States. Although these infections are usually subclinical or self-limited in immunocompetent people, severe disease can be present in susceptible populations (including the elderly or immunocompromised). Here, infections result in hemolytic anemia, thrombocytopenia, hematuria, and renal failure. The mortality rate has been reported to be approximately 5% in such populations. The parasite is located inside red blood cells (RBCs) and classically is identified by a maltese cross formation of the parasites on blood smear preparation. A chronic carrier state can be present in some patients, and, in fact, B. microti is the most frequently transmitted parasitic agent in blood transfusion in this country. Importantly, the parasite remains viable in RBCs for 35 days at 4oC and survives in cryopreserved RBCs. Objective: To describe 18 cases of transfusion-transmitted B. microti between 2005 and 2007. Methods: All cases were identified by the American Red Cross hemovigilance program (ARC HP). Follow-up samples from the donors were tested using an immunofluorescent assay or with real-time polymerase chain reaction (PCR). Results: From an initial 32 suspected cases, 18 cases were classified as definite or probably transfusiontransmitted babesiosis. Most recipients were between the ages of 61 and 84 years, while 2 recipients were <2years-old. Four recipients were asplenic. Five recipients (28%) died within a short period of time after being diagnosed (days to weeks); all 5 had significant preexisting medical conditions. Regarding the donors, 65% were residents of endemic areas (Connecticut, New Jersey, and Massachusetts), and 4 other donors had traveled to endemic areas. In follow-up testing, only 1 of 12 samples tested by PCR was positive, but all donors were positive for antibodies against B. microti. None of the donors recalled symptoms around the time of donation, but some (3 donors) had a recollection of tick bites. Conclusions: Transfusion-transmitted babesiosis is a significant and increasing issue in blood safety. This is highlighted by numerous articles on this topic in the December 2009 edition of Transfusion. The incidence has been estimated at 1 case in 1.1 million RBC units, although this is likely an underestimation. Currently, there is only 1 question on the donor health history questionnaire asking if the donor has a history of babesiosis. Unfortunately, there is no Food and Drug Administration-approved test for B. microti. Reviewer's Comments: This article highlights the need for interventions to reduce patient risk of transfusiontransmitted B. microti. As of now, only directed screening through questionnaires is the best approach to identify at-risk donors. (Reviewer-William A. Kanner, MD).