Acknowledgements: Elena P. Potapkina, Head of Territorial Subdivision of Department of Rospotrebnadzor for Sverdlovsk region in Leninsky, Verkhisetsky, Oktyabrsky and Kirovsky districts of Yekaterinburg for the possibility to conduct a study and develop the methodology; Galie M. Nasybullina, Dr. habil. Med., Professor, Head of department of Hygiene and Ecology of the Federal State Institution of Higher Education ‘Ural State Medical University’ of the Ministry of Health of the Russian Federation for development of concept, resourcing of the study and assistance during the study.

Author contribution: Nasybullina GM, concept and methodology development, resourcing of the study, development of software, performance of the study, approval of the final version; Bayush MA, study performance, conducting statistical analysis, visualization, text preparation and editing; Mironova SS — study performance, conducting statistical analysis, visualization, text preparation and editing.

Compliance with ethical standards: questioning was organized by specialists from the department of Rospotrebnadzor for the Sverdlovsk region and Department of Education in Yekaterinburg using Google Forms. Prior to the questioning, an informed consent to the study was obtained, including the one from children and their parents.