Usefulness of the early molecular diagnosis of Q fever and rickettsial diseases in patients with fever of intermediate duration.

Most cases of fever of intermediate duration (FDI) in Spain are associated with infectious diseases (mainly Q fever and rickettsia infections). In clinical practice, the causal diagnosis of these entities is based on immunodiagnostic techniques, which are of little help in the early stages. Therefore, the aim of this study was to evaluate the usefulness of molecular techniques for the early diagnosis of Q fever and rickettsia diseases in patients with FDI. A PCR method was used to detect the presence of genetic material of Coxiella burnetii and Rickettsia spp. in blood specimens from 271 patients with FDI. The specificity of both techniques is high, allowing diagnosis in cases undiagnosed by specific antibodies detection. These data suggest that the use of molecular techniques, with proper selection of the study specimen, and using appropriate primers is a useful tool in the early diagnosis of the main causes of FDI, especially if serology is negative or inconclusive.