Cases of tick-borne rickettsiosis in Siberia and the Far East are associated with R. sibirica, the causative agent of Siberian tick typhus (STT). In connection with a sharp reduction in the nomenclature of diagnostic products and an increase in the spectrum of species of founding rickettsiae on the territory of Russia, new approaches to the laboratory verification of diagnoses are needed. We present an evaluation of the effectiveness of serological research methods (complement fixation test, indirect immunofluorescence, and ELISA) in patients with tick-borne rickettsioses in areas of different risk of infection with R. sibirica. Patients were diagnosed with STT from the highly endemic territory of the Altai Republic and from the Naziayevsky district of the Omsk region, where natural foci of rickettsioses of the spotted fever group was detected with the circulation of two species of pathogenic rickettsia, R. sibirica and R. raoultii. As a control group, samples of sera from epidemic seasons from clinically healthy people in Omsk were used. To verify the diagnosis of Siberian tick typhus, the use of serological methods is most appropriate, of which the most sensitive is ELISA, which allows detecting antibodies at an earlier time. In the ELISA for confirmation of the diagnosis, the first serum can be examined only on IgM. Investigation of the 2nd serum should be performed in ELISA for the presence of IgM and IgG antibodies with R. sibirica antigen. Reaction of indirect immunofluorescence (RNIF) for the study of paired sera should be conducted with specific antigens of rickettsia circulating in this focus. In laboratories not equipped for setting ELISA, it was recommended to use CFT. When the titer increases in two or more times and IgM and IgG are detected in the second serum, taking into account clinical manifestations, the diagnosis of "Siberian tick typhus" can be considered confirmed.
Keywords: laboratory diagnostics; rickettsiae and rickettsioses; spotted fever group.