Aim of the work: to demonstrate the difficulty of verifying the diagnosis of Q fever with negative results of PCR (DNA of Coxiella burnetii) in the blood and to assess the occurrence of serological markers among patients selected for this study based on a combination of clinical and epidemiological data. Materials and methods: plasma/serum samples of 111 patients according to clinical and epidemiological data studied due ELISA and PCR for specific antibodies to Coxiella burnetii and DNA of pathogen. Additionally, in the presence IgG to C. burnetii phase II, IgG / IgA to phase I and the avidity of specific IgG were studied. Results: the specific antibodies to C. burnetii antigens at negative results of PCR detected in 10 cases. The article provides the description of three clinical cases for demonstration of difficulties of coxiellosis diagnosis with analysis of serological profiles, titers and avidity of antibodies. Conclusion: the results of the study indicate that negative results of PCR testing do not exclude C. burnetii infection. For patients who, according to clinical and epidemiological data, Q fever is not excluded, it is advisable to prescribe a complex of laboratory tests to verify the diagnosis, which includes not only studies of the pathogen’s DNA, but also specific antibodies. To clarify the stage of the disease and reduce the risk of developing complications of coxiellosis, it is necessary to monitor the dynamics of antibody titers to C. burnetii in phase I and II phase states differentially.

Relevance. Q fever in the absence of pathognomic signs is difficult to verify, so the incidence rate of coxiellosis depends on the level of its laboratory diagnosis.Aim. To analyze the incidence of Q fever in the Russian Federation for the time of its official registration (1957–2021) with an assessment of the level of laboratory diagnosis of diseases in different years. The high interest to Q fever in the middle of the last century gave impetus to the commercial production of inactivated Coxiella antigens and kits. The subsequent shortage of economically available diagnostic kits reflected in the official incidence of Q fever. Hypodiagnosis is caused not only by the clinical incidence of infection, but also often by the lack of the possibility of conducting a comprehensive clinical study of the material (detection of antibodies and DNA pathogen). The article presents historical facts for understanding of the rise and incidence of Q fever during the time of its official registration.Conclusions. An analysis of the epidemiological situation should carried taking into account the assessment of the level of diagnosis of Q fever in the regions and the country asa whole. It is necessary to record all newly diagnosed cases of the disease at any stage.

The prevalence of the tick-borne spotted fever group rickettsioses pathogens in ticks collected in Barnaul, the administrative center of Altai Krai, Western Siberia, was studied. The causative agent of tick-borne lymphadenopathy (TIBOLA) Rickettsia raoultii was revealed to be present in 61.9% of the samples from Dermacentor ticks. Moreover, Rickettsia helvetica has been identified in 5.1% of Ixodes ticks.