title: A longitudinal study of Babesia microti infection in seropositive blood donors.
abstract: BACKGROUND
  Babesia infection is caused by intraerythrocytic tick-borne parasites. Cases of transfusion-transmitted babesiosis have been increasingly recognized. To date, no Babesia test has been licensed for screening US blood donors. We conducted a longitudinal study to assess the course and markers of Babesia infection among seropositive donors identified in a seroprevalence study.
  
  
  METHODS
  Eligible donors had B. microti indirect fluorescent antibody (IFA) titers of 64 or greater. Enrollees were monitored up to 3 years, by IFA and three methods for evidence of parasitemia: B. microti nested polymerase chain reaction (PCR) analysis (at two laboratories), hamster inoculation, and blood-smear examination.
  
  
  RESULTS
  Among 115 eligible donors, 84 (73%) enrolled. Eighteen enrollees (21%) had evidence of parasitemia for 30 total specimens (17% of 181), which were collected in 9 different months and tested positive by various approaches: PCR (25 specimens/16 persons), hamster inoculation (13 specimens/8 persons), and blood smear (one specimen positive by all three approaches). Overall, 14 persons had one or more specimen with positive PCR results at both laboratories (12 persons) and/or had parasitologically confirmed infection (eight persons). Three of nine persons who had more than one specimen with evidence of parasitemia had nonconsecutive positives. Several enrollees likely had been infected at least 1 year when their last positive specimen was collected. The final three specimens for seven persons tested negative by all study methods, including IFA.
  
  
  CONCLUSIONS
  Seropositive blood donors can have protracted low-level parasitemia that is variably and intermittently detected by parasitologic and molecular methods. Donor-screening algorithms should include serologic testing and not solely rely on molecular testing.
authors.affiliation: Transmissible Diseases Department, American Red Cross Holland Laboratory, Rockville, Maryland.
authors.forename: David A
authors.initials: DA
authors.lastname: Leiby
authors.forename: Stephanie T
authors.initials: ST
authors.lastname: Johnson
authors.forename: Kimberly Y
authors.initials: KY
authors.lastname: Won
authors.forename: Eva K
authors.initials: EK
authors.lastname: Nace
authors.forename: Susan B
authors.initials: SB
authors.lastname: Slemenda
authors.forename: Norman J
authors.initials: NJ
authors.lastname: Pieniazek
authors.forename: Ritchard G
authors.initials: RG
authors.lastname: Cable
authors.forename: Barbara L
authors.initials: BL
authors.lastname: Herwaldt
mesh_terms: D000328:Adult; D000368:Aged; D000913:Antibodies, Protozoan / Q000032:analysis; D041001:Babesia microti / Q000276:immunology / Q000472:pathogenicity*; D001404:Babesiosis / Q000097:blood* / Q000276:immunology; D001782:Blood Donors / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D018512:Parasitemia / Q000097:blood / Q000276:immunology / Q000469:parasitology
chemical_list: D000913:Antibodies, Protozoan