Babesiosis

Case Definition

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Confirmed case

Laboratory confirmation of infection by the following method with or without clinical evidence of illness1 (can include transfusion transmission):
  • Detection of Babesia species (e.g. Babesia microti, Babesia duncani, or Babesia divergens) DNA in a whole blood specimen by amplification of a specific target Nucleic Acid Amplification Test (NAAT).

Probable case

Laboratory evidence of infection in the form of one of the following:
  • ​Serological evidence of elevated IgG antibodies to B. microti in a single sample by indirect immunofluorescence assay (IFA) or enzyme immunoassay (EIA, if available) where the endpoint titre is ≥ 1:64.
  • Identification of intraerythrocytic Babesia organisms ​by light microscopy in a Giemsa, Wright, or Wright-Giemsa–stained blood smear.
  • Demonstration of a positive B. microti IgG immunoblot result by Centers for Disease Control and Prevention (CDC).
  • Demonstration of a B. divergens total immunoglobulin (Ig) or IgG antibody titre of ≥ 1:256 in an IFA.
  • Demonstration of a B. duncani total immunoglobulin (Ig) or IgG antibody titre of ≥ 1:256 in an IFA.
AND

Clinical evidence of illness1 

OR

A blood donor or recipient epidemiologically linked2 to a confirmed or probable babesiosis case.

1Clinical evidence of illness is characterized by fever and at least one of the following: fatigue, chills, sweats, headache, anorexia, hemolytic anemia, or thrombocytopenia.
2For the purposes of surveillance, epidemiologic linkage between a transfusion recipient and a blood donor is demonstrated if all of the following criteria are met:​
  1. Laboratory evidence of Babesia infection in the recipient and donor.
  2. Transfusion recipient received one or more red blood cell (RBC) or platelet unit(s) within one year before the collection date of the recipient’s positive specimen.
  3. Transfused unit(s) was/were plausibly infectious based on assessment of donor infectivity at time of donation of implicated unit(s).
  4. Transfusion-associated infection in the recipient is considered at least as plausible as tick-borne transmission.