Author contribution: Voroshilina ES — organization of the study, conducting real-time PCR, data analysis, writing the article; Khayutin LV — organization of the study,data analysis, patient selection, writing the article; Kudryavtseva EV, Kovalev VV — statistical processing, data analysis, writing the article; Plotko EE — organization of the study,data analysis, patient selection, writing the article.

Compliance with ethical standards: the study was approved by the Ethics Committee of Ural State Medical University, Federal State Budget Educational Institution of Higher Education under the Ministry of Health of the Russian Federation (Protocol № 7 dated March 28, 2011). All patients signed the informed written consent to participation in the study.