Primary isolation of Ehrlichia chaffeensis from patients with febrile illnesses: Clinical and molecular characteristics

Ehrlichia chaffeensis was sought among patients with a history of tick expo sure and fever, and the accuracy of other diagnostic tests was compared wit h that of primary isolation. Among the 38 patients enrolled, E. chaffeensis was isolated from the blood of 7 (18%) and from cerebrospinal fluid specim ens of 2 of these 7. All 7 patients also were positive by polymerase chain reaction (PCR) of blood, and 6 patients developed diagnostic titers of anti body to E. chaffeensis. The isolates were characterized by molecular analys is of the 16S rRNA gene, the 120-kDa protein gene, and the variable-length PCR target (VLPT) of E. chaffeensis. On the basis of the 120-kDa and VLPT g enotypes, the cerebrospinal fluid and blood isolates from the same patients were identical. This study demonstrates that both PCR and culture of blood for E. chaffeensis have high diagnostic yields. More frequent isolation of E. chaffeensis from patients with infection should further our understandi ng of the pathogenesis of this infection.