Inclusion Criteria:  Adults older than 50 years of age visiting the Health Care Centre with or without signs of upper respiratory tract infection during the study period  Exclusion Criteria:  Living outside of Novi Sad, use of oral antibiotics in the two weeks prior to taking the swab and presence of a confirmed immunodeficiency (hematological malignancies, inherited immunodeficiency, HIV, post-splenectomy status, cancer chemotherapy).