Inclusion Criteria:  Aged >18 years old; Male or female patients; Patients undergoing elective standard diagnostic EGD; Negative polymerase chain reaction (PCR) test on nasopharyngeal swab 24 or 48 hours prior to the test; No anatomical deformity of nose and throat, no known diseases of nose and throat; Signed informed consent  Exclusion Criteria:  Females who are pregnant or lactating.