Acknowledgements: the authors would like to thank Professor OYu Kuznesova, Head of the Family Medicine Department, Mechnikov North-Western State Medical University, for assistance in primary data acquisition; OV Kovaleva, Head of the Outpatient Clinic of the Family Medicine Center, Mechnikov North-Western State Medical University, for assistance in data acquisition and primary data provided.

Author contribution: Liubimova AV — epidemiological data analysis, systematic analysis, manuscript writing; Gasanbekov IM — statistical analysis, preparing illustrations; Meltser AV — technical aspects of the study, discussion, manuscript editing; Lopatin ZV — editing, approving the final version of the article; Sayganov SA — discussion, manuscript editing; Aslanov BI — epidemiological data analysis, manuscript editing.

Compliance with ethical standards: the study was approved by the Ethics Committee of Mechnikov North-Western State Medical University (protocol № 7 of 07 October 2020). The informed consent was submitted by all study participants. the study was approved by the Ethics Committee of Mechnikov North-Western State Medical University (protocol № 7 of 07 October 2020). The informed consent was submitted by all study participants.