A prospective study evaluating the presence of Rickettsia in Danish patients with sarcoidosis

Rickettsia helvetica has previously been proposed as an aetiological agent in sarcoidosis. The purpose of the present study was to detect possible signs of Rickettsia infection in a Danish population of patients with sarcoidosis. Twenty-six patients with newly diagnosed sarcoidosis were prospectively enrolled in the study. The diagnosis was confirmed by biopsy in 18 and by clinical characteristics in 8 patients; 11 patients with different non-sarcoid lung diseases were recruited as controls. We obtained information regarding tick exposure and sarcoid disease manifestations by a structured interview. Evidence of rickettsial infection was assessed by an immunofluorescence assay testing for antibodies towards Rickettsia as well as specific real-time polymerase chain reaction (PCR) on lung biopsy specimens. We performed fluorescent in situ hybridization (FISH) on the biopsies to detect rickettsial and eubacterial rRNA. One sarcoidosis patient had serum rickettsial IgG antibodies above the chosen cut-off level. We found no positive rickettsial PCR or FISH analyses in any of the biopsy specimens. One sarcoid patient sample and 1 control sample contained unidentified bacteria. There was no difference in the reported frequency of tick bite between patients and controls. In conclusion, we found no evidence of Rickettsia being involved in the pathogenesis of sarcoidosis in Denmark.