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Ehrlichiosis
2000 Case Definition

Subtype(s)

  • Human granulocytic ehrlichiosis
  • Human monocytic ehrlichiosis
  • Other or unspecified human ehrlichiosis

Clinical Description

A tick-borne illness characterized by acute onset of fever, headache, myalgia, and/or malaise. Nausea, vomiting, or rash may be present in some cases. Clinical laboratory findings may include thrombocytopenia, leukopenia, and/or elevated liver enzymes. Intracytoplasmic bacterial aggregates (morulae) may be visible in the leukocytes of some patients.

Three categories of confirmed or probable ehrlichiosis should be reported: 1) human ehrlichiosis caused by E. chaffeensis (HME), 2) human ehrlichiosis caused by E. phagocytophila (HGE), and 3) human ehrlichiosis (other or unspecified agent), which includes cases that cannot be easily classified by available laboratory techniques, and cases caused by novel Ehrlichia species such as E. ewingii.

Subtype(s) Case Definition  

Human granulocytic ehrlichiosis

Laboratory Criteria for Diagnosis

  • Demonstration of a four-fold change in antibody titer to E. phagocytophila antigen by IFA in paired serum samples, OR
  • Positive PCR assay and confirmation of E. phagocytophila DNA, OR
  • Identification of morulae in leukocytes, and a positive IFA titer to E. phagocytophila antigen (based on cutoff titers established by the laboratory performing the assay), OR
  • Immunostaining of E. phagocytophila antigen in a biopsy or autopsy sample, OR
  • Culture of E. phagocytophila from a clinical specimen.

Human monocytic ehrlichiosis

Laboratory Criteria for Diagnosis

  • Demonstration of a four-fold change in antibody titer to E. chaffeensis antigen by indirect immunofluorescence assay (IFA) in paired serum samples, OR
  • Positive polymerase chain reaction (PCR) assay and confirmation of E. chaffeensis DNA, OR
  • Identification of morulae in leukocytes, and a positive IFA titer to E. chaffeensis antigen (based on cutoff titers established by the laboratory performing the assay), OR
  • Immunostaining of E. chaffeensis antigen in a biopsy or autopsy sample, OR
  • Culture of E. chaffeensis from a clinical specimen.

Other or unspecified human ehrlichiosis

Laboratory Criteria for Diagnosis

  • Demonstration of a four-fold change in antibody titer to more than one Ehrlichia species by IFA in paired serum samples, in which a dominant reactivity cannot be established, OR
  • Identification of an Ehrlichia species other than E. chaffeensis or E. phagocytophila by PCR, immunostaining, or culture.

Case Classification

Probable

A clinically compatible illness with either a single positive IFA titer (based on cutoff titers established by the laboratory performing the test) or the visualization of morulae in leukocytes.

Confirmed

A clinically compatible illness that is laboratory-confirmed.



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