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Ehrlichiosis (HGE, HME, other or unspecified)
1998 Case Definition
Clinical description
A tick-borne febrile illness most commonly characterized
by acute onset, accompanied by headache, myalgia, rigors and/or malaise;
clinical laboratory findings may include: intracytoplasmic microcolonies
(morulae) in leukocytes of peripheral smear, cerebrospinal fluid or bone
marrow aspirate or biopsy, cytopenias (especially thrombocytopenia and
leukopenia), and elevated liver enzymes (especially alanine aminotransferase
or aspartate aminotransferase).
There are two clinically similar but serologically
distinct forms of ehrlichiosis: human granulocytic ehrlichiosis (HGE)
caused by infection with an Ehrlichia equi-like agent and
found primarily in the upper midwest and northeast, and human monocytic
ehrlichiosis (HME) caused by Ehrlichia chaffeensis infection
and found primarily in the southeastern quadrant of the U.S.
Laboratory criteria for diagnosis
All laboratory testing must be conducted by experienced
personnel with appropriate training and include appropriate controls
and reagents necessary for accurate etiologic diagnosis.
- Fourfold or greater change in antibody titer to
Ehrlichia spp. antigen by immunofluorescence antibody (IFA) test
in acute and convalescent specimens ideally taken four weeks or
more apart. HME diagnosis requires E. chaffeensis antigen
and HGE diagnosis currently requires E. equi or HGE-agent
antigen; or
- Positive polymerase chain reaction (PCR) assay.
Distinct primers are used for the diagnosis of HGE and HME; or
- Intracytoplasmic morulae identified in blood, bone
marrow or CSF leukocytes and an IFA antibody titer >=1:64.
Case classification
Probable: a clinically
compatible case with a single IFA serologic titer >=1:64 or intracytoplasmic
morulae identified in blood, bone marrow or CSF leukocytes
Confirmed: a clinically compatible case that
meets the laboratory criteria for diagnosis
See also:
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