Prevalence of Babesia antibody in a selected blood donor population.

Human babesiosis, a parasitic disease transmitted by the tick, Ixodes dammini, was confined previously to limited areas of the northeastern United States. It is a rare but potentially life-threatening complication of transfusion. Red cells and platelets prepared from asymptomatic donors have been implicated in transfusion-transmitted cases. More cases of babesiosis are being reported as the range of the vector expands in the United States. Blood donors from an endemic area were tested for antibody to Babesia microti during the summer. Only 3.7 percent of the 779 donors were seropositive, compared with 4.7 percent (p greater than 0.05) of donors from a nonendemic area. An epidemiologic survey of seropositive and matched seronegative controls demonstrated no significant differences that would assist in screening donors.