Antimicrobial susceptibility of Ehrlichia phagocytophila.

Human granulocytic ehrlichiosis is a recently described disease caused by an obligate intracellular gram-negative organism recently named Ehrlichia phagocytophila. To expand our knowledge of the susceptibility of E. phagocytophila, we tested six New York State isolates for susceptibility to 12 antimicrobials using an HL-60 cell culture system. All of the isolates were susceptible to doxycycline (MIC, < or =0.125 microg/ml; minimum bactericidal concentration [MBC], 0.125 to 0.5 microg/ml), rifampin (MIC, < or =0.125 microg/ml; MBC, < or =0.125 microg/ml), ofloxacin (MIC, < or =2 microg/ml; MBC, < or =2 microg/ml), levofloxacin (MIC, < or =1 microg/ml; MBC, < or =1 microg/ml), and trovafloxacin (MIC, < or =0.032 microg/ml; MBC, < or =0.032 microg/ml). Isolates were uniformly resistant to amoxicillin, ceftriaxone, erythromycin, azithromycin, clarithromycin, and amikacin. For one strain, the MBC of chloramphenicol was < or =8 microg/ml. These data suggest that quinolone antibiotics and rifampin may be alternative agents for patients with intolerance to tetracyclines.

Survival of the human granulocytic ehrlichiosis agent under refrigeration conditions.

The human granulocytic ehrlichiosis (HGE) agent in infected blood specimens remained viable during refrigeration at 4 degrees C for up to 18 days. These findings suggest that blood specimens submitted for culture may withstand transportation to a remote laboratory. HGE should be added to the list of infections potentially transmitted by blood transfusion.

Serology of culture-confirmed cases of human granulocytic ehrlichiosis.

We evaluated the antibody responses in the sera of 24 patients with culture-confirmed human granulocytic ehrlichiosis (HGE). Antibody titers were measured by an indirect immunofluorescent-antibody assay (IFA) by using a local human isolate as the source of antigen. All patients received appropriate antimicrobial treatment. One hundred five serum specimens collected at baseline and at periodic intervals for up to 14 months were included in the study. Seroconversion was observed in 21 of 23 patients (91.3%) from whom convalescent-phase sera were obtained. Antibodies were first detected at an average of 11.5 days after onset of symptoms. Peak titers (>/=2,560 for 71.4% of patients and >/=640 for 95.2% of patients) were obtained an average of 14.7 days after onset of symptoms. Eleven of 13 patients (84.6%) from whom sera were collected between 6 and 10 months after onset of symptoms were still seropositive, and sera from 5 of 10 (50%) patients tested positive between 11 and 14 months after onset of symptoms. For a subset of 71 serum specimens from 17 patients with culture-confirmed HGE also tested by IFA by using either a human isolate from Wisconsin or an Ehrlichia equi isolate from a horse, there was qualitative agreement for 62 serum specimens (87. 3%). Peak titers were higher, however, with the local human HGE isolate, but the difference was not statistically significant. In summary, most patients with culture-confirmed HGE develop antibodies within 2 weeks of onset of symptoms. Antibodies reach high titers during the first month and remain detectable in about one-half of patients at 1 year after onset of symptoms.