Rickettsia spp and Coxiella burnetii among the Most Frequent Causative Agents of Fever of Intermediate Duration in the North of Spain

The aim was to evaluate the etiologies of Fever of Intermediate Duration (FID) in a prospective study performed at an Infectious Diseases Department in Spain (January 2005-August 2008 and January-July 2010). An infectious cause (62.50% bacteria and 37.50% viruses) was attributed in 77.67% cases, 4.85% were non-infectious cases, and for 17.48% the etiology was unknown. Using immunofluorescence assays (IFA, IgG) and/or PCR targeting 16S rRNA gene and ompA and ompB rickettsial genes followed by sequence analysis, 33 patients (32.04%) showed evidence of spotted fever group Rickettsia infection (Mediterranean spotted fever). IgG antibodies against Coxiella burnetii were detected in 15/103 patients (14.56%) by IFA, and one serum sample showed IgG antibodies against Rickettsia typhi (0.97%). Francisella tularensisspecific antibodies were detected in 1/103 patients (0.97%) using microagglutination test. Based on ELISA or chemiluminiscence assays, Cytomegalovirus (CMV) and EpsteinBarr virus (EBV) infections were the most frequent viral infections (12.62 and 9.71%, respectively), followed by Erythrovirus B-19 infection in 4/103 patients (3.88%) and Human Immunodeficiency Virus (HIV) acute infection in 3/103 patients (2.91%), respectively. In conclusion, Rickettsia spp. and C. burnetii were the most important etiological agents of FID. The empirical use of doxycycline could be appropriate since it is effective for most patients.