The interface between research and the diagnosis of an emerging tick-borne disease, human ehrlichiosis due to Ehrlichia chaffeensis.

Two new ehrlichial species that cause human disease have recently been identified: Ehrlichia chaffeensis and the currently unnamed agent of human granulocytic ehrlichiosis. Our objective was to review data on the clinical presentation, laboratory and epidemiological findings, therapy, and diagnostic procedures of patients with human ehrlichiosis due to E chaffeensis. From 1986 through 1994, 400 case patients were identified from 30 US states. Most patients had a nonspecific illness, characterized by fever and headache. Severe illness and death occurred, primarily in the elderly. Laboratory findings most commonly included leukopenia, thrombocytopenia, and elevated liver function test results. Antibody response was the basis for diagnosis, although polymerase chain reaction testing has been useful in research settings. Empirical treatment with tetracycline or its analogues should be begun as soon as possible after the onset of symptoms. Clinicians need to be alert for this illness when evaluating febrile patients whose history includes possible recent tick exposure.