Reactivity of human sera to different strains of granulocytic ehrlichiae in immunodiagnostic assays

Sera from 35 patients diagnosed with human granulocytic ehrlichiosis in Con necticut were tested by indirect IFA staining methods with 5 strains of Ehr lichia equi or the human granulocytic ehrlichiosis agent to assess the suit ability of different strains in laboratory analyses. Antigens included hors e-derived infected neutrophils (MRK and BDS strains) and human isolates cul tured in human promyelocytic leukemia cells (NCH-1, RCH, and Webster). Of 3 5 sera, 23 (65.7%) reacted to all 5 strains. Seropositivity was highest (97 .1%) in assays that contained the MRK strain from California and lowest (71 .4%) in tests with the NCH-1 strain from Nantucket, Massachusetts, In paral lel testing of 32 sera with the NCH-1 strain by indirect LFA and Western bl ot analyses, results were concordant for 30 samples (93.8%), All strains of ehrlichiae can be used in IFA analyses for antibody detection, but assay s ensitivity varied with the strain used.