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 meas ured 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 base line and at periodic intervals for up to 14 months were included in the stu dy. Seroconversion was observed in 21 of 23 patients (91.3%) from whom conv alescent-phase sera were obtained. Antibodies were first detected at an ave rage of 11.5 days after onset of symptoms. Peak titers (greater than or equ al to 2,560 for 71.4% of patients and greater than or equal to 640 for 95.2 % of patients) were obtained an average of 14.7 days after onset of symptom s. Eleven of 13 patients (84.6%) from whom sera were collected between 6 an d 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 cult ure confirmed HGE also tested by LFA by using either a human isolate from W isconsin or an Ehrlichia equi isolate from a horse, there was qualitative a greement for 62 serum specimens (87.3%). Peak titers were higher, however, with the local human HGE isolate, but the difference,vas not statistically significant. In summary, most patients with culture-confirmed HGE develop a ntibodies 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.