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Aerosols Produced by Upper Gastrointestinal Endoscopy: A Quantitative Evaluation

Sagami, Ryota MD1; Nishikiori, Hidefumi MD1; Sato, Takao MD1; Tsuji, Hiroaki MD1; Ono, Masami MD1; Togo, Kazumi MD2; Fukuda, Kensuke MD2; Okamoto, Kazuhisa MD2; Ogawa, Ryo MD2; Mizukami, Kazuhiro MD, PhD2; Okimoto, Tadayoshi MD, PhD2; Kodama, Masaaki MD, PhD2; Amano, Yuji MD, PhD3; Murakami, Kazunari MD, PhD2

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The American Journal of Gastroenterology: January 2021 - Volume 116 - Issue 1 - p 202-205
doi: 10.14309/ajg.0000000000000983
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Coronavirus disease 2019 (COVID-19) is a global pandemic. During endoscopy, aerosols generated from the nasopharynx of infected individuals because of processes such as reflex vomiting and coughing or contact with contaminated surroundings such as body fluids, especially feces, might be a potential route of transmission (1–5). Aerosols refer to particles in suspension in a gas, such as small droplets in air (6). Considering not only COVID-19 but any respiratory virus, it is important to determine whether endoscopy poses a potential risk of aerosol infection to healthcare workers involved in endoscopy, but it remains unclear (2,5). Endoscopy with high-level personal protective equipment is believed to contribute to reducing the infectious risk; however, if many aerosols are actually produced by endoscopy, only N95 respirators show advantages by blocking 0.3-μm-diameter aerosols by at least 95% (5,7). They should be worn during all endoscopies, considering the substantial risks of aerosol infection, especially from asymptomatic infected individuals (7–9). We reported that a barrier enclosure covering the head of the patient during upper gastrointestinal endoscopy indeed protects against the widespread dispersal of splash and aerosols and recommended it as additional protection to the standard personal protective equipment (10). In this study, whether endoscopy produces aerosols was quantitatively analyzed using this enclosure.


A newly developed plastic enclosure, “endoscopic shield,” is used during routine endoscopy at our facility during the COVID-19 pandemic (10). Patients are placed in a left lateral position, with their heads covered by this enclosure. The facial side of the enclosure contains 2 small holes, with the endoscope inserted through the upper hole (10). Endoscopists are positioned directly opposite the patient's face (10). Aerosols of patients undergoing endoscopy with the 9.9-mm-diameter GIF-H290 (Olympus Medical Systems, Tokyo, Japan) and those not undergoing endoscopy, control patients, enrolled from among healthy volunteers of the facility, were measured from the lower hole by a Handheld Optical Particle Counter (MODEL 3889; Kanomax Japan, Osaka, Japan) that suctioned air at 2.83 L/min. The interunit higher precision was 50% ± 20% for 0.3-μm aerosols and 100% ± 10% for 0.5-μm aerosols compared with standard aerosols (11,12). Aerosols of patients undergoing endoscopy were measured for 60 seconds, 60 seconds after the placement of the enclosure (before endoscopy), 120 seconds after the start of endoscopy (during endoscopy), and after the completion of endoscopy (after endoscopy) (Figure 1). Aerosols of control patients were measured according to the same time schedule with simulated endoscopy, which was calculated from the average procedure durations of patients undergoing endoscopy. Aerosols with diameters of 0.3–10 μm were evaluated considering the standard filtration efficiency test on aerosols <0.3 μm (7) and small aerosols of diameter <5–10 μm that follow airflow streamlines with the possibility of transmission containing coronavirus 2 (6,8).

Figure 1.:
The schema of the position of the endoscope and aerosol counter with and without endoscopy and the schedule of aerosol measurements in both groups: patients undergoing endoscopy (a) and control patients (b). Simulated endoscopy was assumed to be performed for the average procedure length (280 seconds) of patients undergoing endoscopy.

Between May 12 and May 20, 2020, patients undergoing upper gastrointestinal endoscopy with the enclosure and conscious sedation by midazolam in a positive-pressure room were enrolled. Baseline characteristics and procedure-related factors based on the consensus of 2 or more of 3 nurses were evaluated. Moderate sedation was defined by Ramsay scores (13). Patients whose endoscopy was suspended because of strong movement during endoscopy and required additional sedative agents to continue endoscopy were excluded.

The primary outcome was to assess the changes of aerosols before, during, and after endoscopy and compare their trends in the endoscopy and control groups. The secondary outcome was to analyze the relationships among patients' characteristics, procedure-related factors, and increased aerosols during endoscopy using Student's t test or logistic regression analyses.

This study was registered in the University Hospital Medical Network Clinical Trials Registry (UMIN 000040520) after the approval by the Institutional Review Board of Oita San-ai Medical Center (IRB No. 020004K).


Although 105 consecutive patients undergoing endoscopy and 90 control patients were enrolled, 2 of the 105 endoscopy patients were excluded from the analysis because of their requiring additional sedation. Based on the average procedure times of endoscopy, the duration of simulated endoscopy was 280 seconds. For aerosol changes during and after endoscopy compared with before endoscopy, aerosols increased significantly in the endoscopy group than the control group (P < 0.001, P < 0.001, respectively). The increased aerosol count was also significantly higher during endoscopy than in control patients (P = 0.006) (Table 1). In the endoscopy group, 60 patients were classified as having increased aerosols when the values of aerosols were more than +2 SDs compared with the control group. Body mass index and burping were significant factors related to increased aerosols during endoscopy on both univariate (P = 0.020 and 0.018, respectively) and multivariate logistic regression analyses (P = 0.033 and 0.025, respectively) (Table 2).

Table 1.:
Patients' baseline characteristics and comparison of changes in aerosol counts in the endoscopy and control groups
Table 2.:
Patients' baseline characteristics and comparison of procedure-related factors between patients with increased and without increased aerosols during endoscopy in the endoscopy group


Many worldwide societies of gastroenterology suspect that endoscopy must be an aerosol-generating procedure (2,5). Objectively, the patient may generate aerosols because of processes such as coughing (2,5,14). This study confirmed quantitatively that upper gastrointestinal endoscopy is certainly an aerosol-generating procedure by measuring 0.3–10-μm aerosols. In another study, the size of the COVID-19 virus was 0.06–0.14 μm, with nanospikes coated on its spherical viral envelope with heights of 0.09–0.12 μm attached to a larger carrier and becoming airborne with a size of 0.1–0.3 μm (7). To shield healthcare workers from any respiratory viral infection because of aerosols during endoscopy, N95 respirators should be worn to block small (<5 μm) aerosols (15). In this study, the level of sedation did not affect aerosol increase, but burping was significantly related. More careful insufflation and adequate sedation may prevent burping and minimize the aerosol-related risk (14).

Small aerosols (<10 μm) are easily scattered because they are more susceptible to ambient airflows, strong cross-flow, or natural ventilation. Therefore, they cannot stay in a certain air place for long (6). Measurement of aerosols in the room may not be suitable because they are greatly affected by environmental airflows. In this study, aerosols in the enclosure that are unlikely to be affected by airflows were evaluated, and contaminated air was captured to some extent. The enclosure may provide additional protection during endoscopy. However, only a relatively small sample size was evaluated; therefore, a prospective study with a larger sample size is needed.

In conclusion, endoscopy definitely generates aerosols. To prevent infection, additional protection as an adjunct to standard infection protection is needed, such as an enclosure and adequate conscious sedation.


Guarantor of the article: Ryota Sagami, MD.

Specific author contributions: R.S.: served as a project principal investigator and supervised the overall conduct of the study; developed the study concept and design; performed data curation, formal analysis, validation, and visualization; drafting of the manuscript; and critical revision of the manuscript. H.N.: assisted with the study concept and design, material support, acquisition of data and drafting of the manuscript. T.S., H.T., M.O., K.T., K.F., K.O., R.O., K.M., T.O., M.K.: assisted with the study concept and design, acquisition of data, and drafting of the manuscript. Y.A.: performed supervision, writing review, and editing of the manuscript. K.M.: performed project administration, supervision, writing review, and editing of the manuscript. All authors provided the final approval of the article before submission.

Financial support: None to report.

Potential competing interests: Y.A. received the lecture fee from Takeda Pharmaceutical Co., Ltd.


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Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of The American College of Gastroenterology