Droplet nuclei are generated during colonoscopy and are decreased by the use of carbon dioxide and water immersion technique

The COVID-19 pandemic has raised concerns on whether colonoscopies (CS) carry a transmission risk. The aim was to determine whether CS are aerosol-generating procedures.

This was a prospective observational trial including all patients undergoing CS at the Prince of Wales Hospital from 1 June to 31 July 2020. Three particle counters were placed 10 cm from each patient's anus and near the mouth of endoscopists and nurses. The particle counter recorded the number of particles of size 0.3, 0.5, 0.7, 1, 5, and 10 μm. Patient demographics, seniority of endoscopists, use of CO₂ and water immersion technique, and air particle count (particles/cubic foot, dCF) were recorded. Multilevel modeling was used to test all the hypotheses with a post-hoc analysis.

A total of 117 patients were recruited. During CS, the level of 5 μm and 10 μm were significantly higher than the baseline period (P = 0.002). Procedures performed by trainees had a higher level of aerosols when compared to specialists (0.3 μm, P < 0.001; 0.5 μm and 0.7 μm, P < 0.001). The use of CO₂ and water immersion techniques had significantly lower aerosols generated when compared to air (CO₂ : 0.3, 0.5, and 0.7 μm: P < 0.001; water immersion: 0.3 μm: P = 0.048; 0.7 μm: P = 0.03). There were no significant increases in any particle sizes during the procedure at the endoscopists' and nurses' mouth. However, 8/117 (6.83%) particle count tracings showed a simultaneous surge of all particle sizes at the patient's anus and endoscopists' and nurses' level during rectal extubation.

Colonoscopy generates droplet nuclei especially during rectal extubation. The use of CO₂ and water immersion techniques may mitigate these risks.