Seroprevalence of Babesia microti in blood donors from Babesia-endemic areas of the northeastern United States: 2000 through 2007.

Background: Current estimates of 70 cases of transfusion-transmitted Babesia microti, with 12 associated deaths, suggest that Babesia is a growing blood safety concern. The extent of Babesia infections among blood donors has not been well defined. To determine how common exposure to B. microti is among blood donors, a seroprevalence study was undertaken in the American Red Cross Northeast Division.

Study Design And Methods: Blood donations at selected blood drives in Connecticut and Massachusetts (2000 through 2007) were tested for the presence of immunoglobulin (Ig)G antibodies to B. microti using immunofluorescence assay. Geographic and temporal trends of B. microti seroprevalence were estimated for donor's zip code of residence.

Results: Overall, a 1.1% seroprevalence was identified in Connecticut, with the highest levels found in two Southeastern counties (Middlesex and New London). Observed seroprevalence for offshore islands of Massachusetts was 1.4%. Seropositive donations were identified from donors residing in all eight counties in Connecticut and three counties in Massachusetts. Although a seasonal peak was found between July and September, seropositive donations were identified in every month of the year.

Conclusions: Foci of statistically higher B. microti seroprevalence among blood donors were observed; however, B. microti transfusion transmission risk exists for blood collected throughout Connecticut and portions of Massachusetts. Similarly, a seasonal peak was identified; nevertheless, seropositive donations were found year-round. Thus, geographic and/or seasonal exclusion methods are insufficient to fully safeguard the blood supply from Babesia transmission. Steps should be taken to reduce risk of transfusion-transmitted B. microti, perhaps through implementation of year-round, regional testing.