Because of the nonspecific clinical presentation, empirical therapy should be started as soon as possible after the onset of symptoms. Therapy should not be delayed until a serologic diagnosis is confirmed, since this may take several weeks. The HGE agent has been cultured from 3 patients using HL60 cells. Diagnosis of acute infection can only be made by demonstrating a significant rise in antibody level between acute and convalescent specimens where both tests are done in the same laboratory at the same time. Appearance of an IgM antibody response normally occurs 7-14 days after the onset of disease.
Testing immediately post-exposure is of no value without a later convalescent specimen.
While the presence of IgM antibodies suggest current or recent infection, low levels of IgM antibodies may occasionally persist for more than 12 months post-infection. Such a residual IgM response may be distinguished from early IgM response to infection by testing sera from patients 2-3 weeks later for changing levels of specific antibodies. A single IgM result should be interpreted with caution. They are prepared by harvesting leukocytes from experimentally infected livestock. Specific oligonucleotide PCR primers have been designed on the basis of the nucleotide sequences of the 16S rDNA for E. chaffeensis and the HGE agent.