Outcome of diagnostic tests using samples from patients with culture-proven human monocytic ehrlichiosis: Implications for surveillance

We describe the concordance among results from various laboratory tests usi ng samples derived from nine culture-proven cases of human monocytic ehrlic hiosis (HME) caused by Ehrlichia chaffeensis, A class-specific indirect imm unofluorescence assay for immunoglobulin M (IgM) and IgG, using E. chaffeen sis antigen, identified 44 and 33% of the isolation-confirmed HME patients on the basis of samples obtained at initial clinical presentation, respecti vely; detection of morulae in blood smears was similarly insensitive (22% p ositive). PCR amplifications of ehrlichial DNA targeting the 16S rRNA gene, the variable-length PCR target gene, and the groESL operon were positive f or whole blood specimens obtained from all patients at initial presentation . As most case definitions of HME require a serologic response with compati ble illness for a categorization of even probable disease, PCR would have b een required to confirm the diagnosis of HME in all nine of these patients without the submission of a convalescent-phase serum sample. These data sug gest that many, if not most, cases of HME in patients who present early in the course of the disease may be missed and underscore the limitations of s erologically based surveillance systems.