inclusion criteria: age of 18 years or more; negative test (pcr) for sars-cov-2 infection; the absence of clinical manifestations of a respiratory infection; contact with patients with laboratory and / or clinically confirmed sars-cov-2 infection; signed informed consent to participate in the study.

inclusion criteria: age of 18 years or more; negative test (pcr) for sars-cov-2 infection; the absence of clinical manifestations of a respiratory infection; contact with patients with laboratory and / or clinically confirmed sars-cov-2 infection; signed informed consent to participate in the study.

inclusion criteria: 1. age of 18 years or more; 2. negative test (pcr) for sars-cov-2 infection; 3. the absence of clinical manifestations of a respiratory infection; 4. contact with patients with laboratory and / or clinically confirmed sars-cov-2 infection; 5. signed informed consent to participate in the study.

inclusion criteria: 1. age of 18 years or more; 2. negative test (pcr) for sars-cov-2 infection; 3. the absence of clinical manifestations of a respiratory infection; 4. contact with patients with laboratory and / or clinically confirmed sars-cov-2 infection; 5. signed informed consent to participate in the study.