Expelled Larger Droplets During Upper Endoscopy and Colonoscopy Are Transmission Risk for COVID-19

Internal view of the intestinal walls. Colonoscopy is the endoscopic examination of the large bowel and the distal part of the small bowel with a camera on a flexible tube. 3d render
Researchers developed a portable optical instrument to assess the droplet-generating risk of endoscopy procedures.

Large droplets expelled by patients during upper endoscopy and colonoscopy procedures pose a risk for COVID-19 transmission to nearby healthcare workers, investigators reported in Gastroenterology.

Researchers developed a portable optical instrument that can distinguish liquid droplets from solid particles to assess the droplet-generating risk of endoscopy procedures, as well as measure the size and quantity of fast-flying droplets in the clinical setting. The instrument measured droplets from 10 patients who had an upper endoscopy and 10 patients who had a colonoscopy.

The study authors measured consecutive procedures in 1 room for 2 days, taking 3 measurements for each patient — 1 time corresponding with the procedure duration and the other 2 times corresponding with controls. The patient and staff were present in the procedure room during the preprocedure control, but the endoscope had not been inserted into the patient. During the postprocedure control, the endoscope had been removed from the patient, although the staff and patient were present.

The data were analyzed after the scattering events that occurred during the procedure and controls were extracted. Most detected droplets had diameters ranging from 40 μm to 50 μm.

The number of scattering events, including droplets and particles, was considerably higher for both controls, compared with the procedures. Regarding droplets that pose a transmission risk, however, significantly more were observed in the procedures compared with controls.

A higher number of droplets were measured during colonoscopy procedures compared with upper endoscopy procedures (4.0 × 10-2 mm-2 vs 2.8 × 10-2 mm-2, respectively). After adjustment for procedure duration, more droplets per unit time were observed during upper endoscopies compared with colonoscopies (3.6 × 10-3 mm-2 × min-1 vs 1.9 × 10-3 mm-2 × min-1, respectively), although the differences were not statistically significant. The procedures had a similar size distribution, with a slightly larger spread occurring during colonoscopies.

The investigators determined that about 500 liquid droplets could be produced during an upper endoscopy, and upper endoscopy procedures could potentially produce about 6500 viral copies per procedure.

“Our results have several important clinical implications,” stated the study authors. “First, the positioning of our device shows that these droplets can reach nearby healthcare workers. Second, while the risk of COVID-19 transmission during upper endoscopy has been well recognized, our findings suggest that transmission via droplets during colonoscopy is also possible,” they noted.

The researchers also found marked variations in droplets produced by patients, with 1 patient from the colonoscopy group and 1 from the upper endoscopy group accounting for about half of the total droplets produced. The patient with the upper endoscopy was not wearing a procedural oxygen mask, though 6 patients were.

Unmasked patients produced an average of 2.75 times more droplets than the masked patients. Low numbers of droplets were observed for some patients in the masked and unmasked groups. For the colonoscopy patient who produced the most droplets, the droplets were dispersed throughout the procedure. However, for the patient with the upper endoscopy, all droplets occurred in one 33-second period and did not occur during coughing or endoscope insertion or removal.

“To our knowledge, this is the first measurement of large droplets, which pose the biggest transmission risk, in the clinical setting,” commented the investigators. “To minimize droplet exposure, we suggest only essential personnel remain close to the endoscope operator during the procedure,” they concluded.


Coughlan MF, Sawhney MS, Pleskow DK, et al. Measuring droplets expelled during endoscopy to investigate COVID-19 transmission risk. Gastroenterol. Published online July 16, 2021. doi: 10.1053/j.gastro.2021.07.013