Frequency and magnitude of seroreactivity to Babesia microti in 245 patients diagnosed by PCR in New York State

Multiple methodologies have been used to detect antibodies to Babesia microii. Use of an indirect immunofluo-rescence assay (IFA) has been the most widely used approach, but IFAs have varied as to which antibody class or dasses are being detected and in regard to cutoff titers. In this study, 245 different patients with polymerase chain reaction (PCR)-confirmed B. microti infection were tested by a polyvalent TA using serum collected within 3 days of the date the blood sample for PCR testing was obtained. Of the 245 patients, 243 (992%) had a positive serologic test result (i.e., >= 1:64). Of the 243 patients who were seropositive, 242 (99.6%) had a titer of >= 1:256, 236 (97.1%) had a titer of >= 1:512, and 210 (86.4%) had a titer of >= 1:1024. In conclusion, high titer seropositivity based on a polyvalent IFA is to be expected at the time of KR confirmation of active babesiosis in clinical practice. (C) 2020 Elsevier Inc. All rights reserved.