In our simulation (Supplementary Video 1), transnasal endoscopy was performed on a mannequin with and without a surgical mask (PRO-LINE, American Society of Testing and Materials Level 1 mask; A.R. Medicom Inc., Ltd., Kobe, Japan), using an ultrathin endoscope (GIF-XP290N; Olympus Medical System, Tokyo, Japan). Coughs were simulated using a 0.4 MPa pressure accumulation sprayer containing 10 mL of fluorescent dye [3-5], and the spread of the scattered dye droplets was visualized under ultraviolet light.

Following the procedure performed without a surgical mask, the dye was found on the endoscopist’s gloves, upper chest, abdomen, and shoe covers (Fig. 2A), and floor contamination of up to approximately 1.5 m away from the bed was observed. When transnasal endoscopy was performed with a surgical mask, the simulated cough contaminated only the inner surface of the mask (Fig. 3), with no detectable dye deposits on the endoscopist (Fig. 2B) or the floor. For clinical validation, 732 patients underwent screening transnasal endoscopy while wearing a mask. During those procedures, vital signs were unaffected and no problems were encountered.

This new and safer method completely covered the examinee’s mouth with a surgical mask and prevented the spread of aerosol droplets. Transnasal endoscopy is well tolerated, and is also a valuable diagnostic tool. Furthermore, transnasal endoscopy can reduce pharyngeal stimulation, resulting in less coughing and reduction of the vomiting reflex than occurs during per-oral endoscopy. Therefore, we propose the adoption of this method as the “new normal” for endoscopy following the COVID-19 pandemic.