Introduction
Evidence for modes of transmission of SARS-CoV-2 remains controversial. In 2020, at
the beginning of the pandemic, extreme safety precautions were taken to prevent direct
and indirect droplet transmission through fomites. These recommendations were implemented
to prevent the spread of the virusfrom patients to health care professionals (HCPs)
and from HCPs to patients, especially during digestive endoscopy [1]. Some studies suggested the potential for airborne transmission in specific environments,
mainly poorly ventilated indoor or health care facilities [2]. The spread of SARS-CoV-2 has been compared to that of other viruses such as SARS-Cov1
and the measles, and also other microorganisms such as tuberculosis and fungi [3]
[4]. However, separating SARS-CoV-2 transmission into the dichotomy of droplets vs airborne
transmission has been shown to be artificial. The switch from droplet to airborne
precautions fed the controversy regarding respiratory protections to prevent transmission
of SARS-CoV-2.
Recently, assessment of air contamination by SARS-CoV-2 in hospital settings has shown
that air near and distant from contaminated patients may carry viral RNA [5]. It has also been suggested that aerosol transmission is increased with the new
variants (alpha and delta), underscoring the need to prevent all methods of aerosolization
in hospitals, and particularly in endoscopy units [6]. During aerosol-generating medical procedures, the production of both airborne particles
and droplets may increase the risk of infection. Anesthesiology procedures, especially
with orotracheal intubation, and upper digestive endoscopies, can generate aerosols
favoring the transmission of the virus in the endoscopic room and especially in the
close environment of patients and HCP [7]
[8]. Therefore, good compliance with procedures and protocols designed for the safety
of patients and HCPs is essential in endoscopy rooms. Recently it has been shown that
rates of SARS-CoV-2 transmission during gastrointestinal endoscopy was low but transmission
was possible [9]
[10].
Considering the way gastrointestinal columns were built, air circulation in the gastrointestinal
light source box and endoscope could be implicated in airborne transmission of microorganisms.
Small viral particles or other microorganisms could contaminate the air used to inflate
the gastrointestinal tract via the endoscope, which comes from the light box of the
endoscopic column. Indeed, the air pump, which has no high-efficiency particulate
air (HEPA) filter, is not accessible for sterilization/decontamination. This pump
is used to inflate air in the gastrointestinal tract through the air channel of the
endoscope and through the water channel after inflation of air in the water tank [11]. The incoming air is aspirated in the light box and then expelled from the box by
two or three fans with a very high flow (4 to 5 m3/min) [11]
[12]. As proposed by Matteo et al, [13] this contamination route must be considered and the development of modified ventilation
systems seems necessary to reduce as much as possible the putative risk of spreading
the virus in an endoscopy room.
Based on those weaknesses, the ENDOBOX SC was developed to protect both patients and
HCPs from airborne virus transmission through the endoscopic system.
Methods
New material: Endobox SC
Air circulation in the light box and the endoscope is illustrated in [Fig. 1]. Putative microorganism circulation in the light source and the environment from
a hypothetical contaminated patient is illustrated in [Fig. 2]. The ENDOBOX SC is a 600 × 600mm cube made of transparent Plexiglas (8-mm thickness).
The ENDOBOX SC has been designed to hold all types of machines used during gastrointestinal
endoscopy and leave a 100-mm space between a machine and the walls of the ENDOBOX
SC to allow for air circulation ([Fig. 3]). On the back of the ENDOBOX SC, a dedicated port was created to connect the light,
the processor box with electrical current, and the screen. Another port was made to
connect the ENDOBOX SC to the medical air system. Medical air is present in all endoscopy
units to help anesthesiologists during the intubation and ventilation period. It creates
a constant and microorganism-free air circuit. The ENDOBOX SC uses the “medical air”
to inflate the digestive tract and to decrease the temperature induced by microprocessors
or by the lamp (ie 323 °C for a Xenon lamp). The airflow of medical air is controlled
by a pressure gauge and is then blown in the box through a multi-hole PVC ramp ([Fig. 4]). The ENDOBOX SC has a fan on each lateral side (120 × 120 mm; Corsair AF120; 12V;
1500 RTW/mn) to direct medical air outside the box into the endoscopic room. Such
a mechanism allows a positive flow from inside to outside. The front of the ENDOBOX
SC has adapters to enable it to be connected to endoscopes from any manufacturers
([Fig. 3] and [Fig. 4]), and to enable a connection between the light box and the pipe of the endoscope
and setting of the dashboard of the light and the processor box. A gasket ensures
that the ENDOBOX SC is airtight.
Fig. 1 Putative microorganism circulation in the light source and the environment of the
endoscopic room.
Fig. 2 Circulation of air into a digestive endoscope showing the origin of air.
Fig. 3 a Anterior and b posterior views of the ENDOBOX SC. The posterior view of the ENDOBOX SC shows a multi
holes PVC ramp to control the pressure inside c the box.
Fig. 4 Circulation of medical air from the wall outlet to the ENDOBOX SC, the light box
and the endoscope, showing the absence of potential contamination using the medical
air from the endoscopic room.
Procedures
The ENDOBOX SC was developed to create a virus-free zone considering the potential
for airborne transmission of a virus. Recently it hs been shown that there is aerosolization
of virus during esophagogastroduodenoscopy. The weakness of the box is the risk of
a major increase in temperature inside the box caused by the light source or the microprocessors.
The light source contains a forced-air cooling system to maintain a stable temperature
in the middle of the box (25 °C). The air used by the forced-air cooling system is
sucked from the closed environment of the patient through aeration ports, located
close to the light source and evacuated out of the box by several fans [11]
[12]. The volume of air that goes through the light source box may be very high (4 to
5 m3/minute ie 240 to 300 m3 for a 1-hour examination) [11]. As illustrated in [Fig. 3], an Eluxeo system (FUJIFILM) was used to test the ENDOBOX SC. The Eluxeo System
was placed in the ENDOBOX SC with the light box, the processor box, and the endoscopic
ultrasound box. The position of the Eluxeo box conformed to manufacturer recommendations
(100-mm distance between the system and each side of the ENDOBOX SC to allow airflow).
The ENDOBOX SC was used for 3 hours with all different types of light, with either
standard or ultrasound endoscopes. Variations in temperature inside the ENDOBOX SC
were continuously measured.
A two-step procedure was performed. The ENDOBOX SC was not connected to the medical
air during the first procedure: The endoscope pipe was connected to the light box
and the light system of the endoscope was on. The ENDOBOX SC was first challenged
without the use of fans in clinical conditions for 15, 30, 45, 60, 120, and 180 minutes.
The second procedure corresponded to “optimal” utilization of the ENDOBOX SC. The
device connected to the medical air, the fans were on, the endoscope pipe was connected
to the light box, and the light system of the endoscope was on. The ENDOBOX SC was
evaluated in clinical conditions for 15, 30, 45, 60, 120, and 180 minutes. During
both procedures, temperature was constantly monitored to prevent computer damage.
The procedure was to be stopped if the variation in temperature was more than ± 20 °C
or if the temperature inside the box was higher than 35 °C.
Results
The ENDOBOX SC was tested to evaluate the increase in temperature in clinical conditions
in two steps. During the first procedure, the procedure was interrupted after 40 minutes
due to a rapid increase in temperature. The temperature reached 35 °C in 40 minutes,
justifying an interruption of the test. During the first 30 minutes, the temperature
increased from 18 °C to 31° with a LED system. The test was performed three times
with similar results.
During the second procedure, the fans were on and the ENDOBOX SC was connected to
the “medical air” system. During the overall procedure, there were small variations
in temperature inside the ENDOBOX SC from 21 °C to 26 °C (± 5 °C) 1 hour after the
beginning of the procedure, confirming that medical air could be used safely. The
temperature was stable during the 3-hour procedure.
Discussion
ENDOBOX SC was developed to eliminate the potential risk of transmission of viruses
and other microorganisms associated with the air circulation system used during gastrointestinal
endoscopic procedures and also to allow ventilation of the system to limit an increase
in temperature. The ENDOBOX SC allows access to all necessary connections to the endoscopy
columns, creating a microorganism-free “zone” and positive pressure volume, which
prevents potential contamination from microorganisms and avoids an increase in temperature
levels induced by light and processors.
Recently it has been shown that rates SARS-CoV-2 transmission during gastrointestinal
endoscopy are low but transmission is possible [10]. In that prospective study of 2440 patients, 30 (1.27 %) patients presented with
COVID-19 symptoms in the 2 weeks following gastrointestinal endoscopy, 16 (0.65 %)
of whom tested positive for SARS-CoV-2. Only three cases (0.12%) were attributed to
transmission from endoscopy attendance, because no other more likely source of transmission
was identified on direct questioning by the local care team [10]. Mechanisms of transmission are still unclear but could be related to air transmission
of the virus. Indeed, viable SARS-CoV-2 has been found in hospital air [14], on a ventilator monitor close to an endoscopic system, on the floor beneath patients’
beds, and in one case in an endoscope [15]. Some medical or surgical procedures increase transmission risk for respiratory
pathogens because they directly generate aerosols or during tracheal intubation. Aerosol
transmission of certain diseases is biologically plausible when: (1) infectious aerosol
are generated from an infector; (2) the pathogen contained in the aerosol in the aerosols
remained viable in the air; and (3) the target tissues are accessible to the aerosols
where the pathogens initiates infection [16]. All endoscopy rooms are indoor places. Many indoor places are poorly ventilated.
Ventilation in those rooms helps to increase air circulation and meantime increase
the risk of airborne transmission. To reduce the aerosol concentration and spread
in an endoscopy room, some authors have proposed using box fan air cleaners [17]. Such procedures have been tested in a classroom where the overall risk is different
from endoscopy unit. However, gastrointestinal and specifically upper endoscopies
have unique qualities, in relation to other endoscopic or surgical procedures.
First, esophagogastroduodenoscopy is performed through the mouth or nose (nasogastroscopy).
Several recent proof-of-concept studies have reported increased levels of aerosol
measured during esophagogastroduodenoscopy and concluded that the procedure increased
the risk of aerosol-generating contamination [7]
[18]. It has been shown recently that patients who coughed during the procedure (60 %)
produced a very high number of particles. Considering that any emitted plumes of aerosol
may contain viable viruses or microorganisms, it creates a potential risk of exposure
for endoscopists or HCPs. In addition, tracheal intubation performed during endoscopic
procedures could generate microorganism aerosols.
Second, gastrointestinal endoscopes are able to insufflate air inside the lumen of
the gastrointestinal tract. This air is insufflated directly in the gut by a pump
through the air channel or indirectly through the water channel of the endoscope because
air is used to propel water from the water tank to the tip of the endoscope [11]. Therefore, air contaminated by viruses, fungi, tuberculosis or other bacteria could
lead to contamination of the air circulation system and the air pump of the light
source. The air circulation system could become an inaccessible niche for microorganisms,
which could be able to contaminate other patients, because the air pump cannot be
routinely cleaned. In such cases, contamination of the air circulation system of the
light source or the air pump could contaminate a patient during an endoscopic procedure,
despite negative virological and bacterial testing after careful disinfection of an
endoscope with peracetic acid [19]. Meanwhile, aspiration of “contaminated” air in the system (light or processor box)
may also result in contamination of all future patients [20].
Third, as described by Klompas et al [21], other factors seemed to play an important role in the occurrence of SARS-CoV-2
infection, such as the proximity between patients and HCPs, the proximity between
patients and the endoscopic system, the duration of exposure to the microorganism,
and ventilation of the room. During gastrointestinal endoscopies, there is close proximity
between patients, who do not wear masks during the procedure, the HCP and the endoscopic
system, allowing for transmission of an aerosolized particle of virus from patients
to HCP or to the endoscopy system, which cannot be cleaned between procedures.
Fourth, colonoscopy could also be an aerosolized procedure, as it has been described
during colonic biopsy removal for bacteria and because SARS-CoV-2 or other microorganisms
are present in fecal samples [22]
[23].
Conclusions
ENDOBOX SC enables access to all necessary connections to the endoscopy columns and
creates a sterile and positive pressure volume, which prevents potential contamination
from microorganisms to patients and to HCPs. Because there is a potential risk of
contamination of patients by microorganisms in the air circulation system of endoscopes,
it appears worthwhile to evaluate different strategies to mitigate the risk of air
transmission. The use of the ENDOSBOX SC system could be an option and deserves further
study.
