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.
Laboratory criteria for diagnosis
HME:
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.
HGE:
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.
Ehrlichiosis ,human, other or unspecified agent:
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.