Inclusion Criteria:  Adults (over 18 years) and children (3-18 years) of both sexes; Patients able and willing to sign an informed consent to participate in the study (parents of children younger than 18 years old will be allowed to give an informed consent on behalf of their children). Patients presenting with a new onset of at least two of listed acute respiratory tract infection symptoms within the last 5 days: cough, purulent sputum, breathlessness, core temperature above 38°C. Patients who first visit a GP with these symptoms within the first 5 days from the onset of symptoms and was not previously treated with antibiotics during the last month.  Exclusion Criteria:  Age up to 3 years; Patient refusal to participate in the study (or patients' parents); Children under full State care (orphans, children left without parental care); Treatment with antibiotics during the last month; Patients with subcutaneous emphysema, with damaged skin on the surface of the chest, with drainage in the pleural space, patients undergoing mechanical ventilation; Presence of other known chronic lung conditions such as asthma, COPD, tuberculosis, cystic fibrosis or bronchiectasis; Mental illness, other known acute diseases or known chronic decompensated diseases, such as a known active malignancy or severe heart failure. Other known ongoing infection.