With a commercially available particle counter, we can differentiate the particle counts of different sizes in different areas of the endoscopy room. An increase from baseline particles of < 5um during or after the procedure would suggest that the procedure is an AGP.

In this study, the particle counter from Met One Instruments model GT-526S will be used. A particle sizer is placed within 10cm of the anus, at the level of the endoscopists' face and at the level of the endoscopy nurse assistant's face The change in the particles of different sizes would be simultaneously recorded. The results of these three locations are compared to baseline and compared with each other

Currently, the term droplet is often taken to refer to droplets >5 microns (μm) in diameter that fall rapidly to the ground under gravity, and therefore are transmitted only over a limited distance (e.g. ≤1 m). In contrast, the term droplet nuclei refers to droplets ≤5 μm in diameter that can remain suspended in air for significant periods of time, allowing them to be transmitted over distances >1 metre. With a commercially available particle counter, we can differentiate the particle counts of different sizes in different areas of the endoscopy room. An increase from baseline particles of < 5um during or after the procedure would suggest that the procedure is an AGP.

In this study, the particle counter from Met One Instruments model GT-526S will be used. The study will be conducted in the Prince of Wales Hospital endoscopy centre. A particle sizer is placed within 10cm of the anus, at the level of the endoscopists' face and at the level of the endoscopy nurse assistant's face The change in the particles of different sizes would be simultaneously recorded. The results of these three locations are compared to baseline and compared with each other.

Inclusion Criteria:

- All patients who are planned for colonoscopy in the Prince of Wales Hospital, Hong kong

Exclusion Criteria:

• Patients where a flexible sigmoidoscopy was plannned Patients where the procedure was done in a negative pressure room Patients where the procedure was done in an endoscopy room other than the designated rooms Patients where the procedure was done under general anaesthesia

All patients who are planned for colonoscopy in the Prince of Wales Hospital, Hong kong.