Using vaporized hydrogen peroxide for anhydrous disinfection of gastrointestinal endoscopes

Abstract

BACKGROUND

Current disinfection methods for gastrointestinal endoscopes consume a significant amount of water resources and produce a large volume of waste.

AIM

To achieve the objectives of efficiency, speed, and cost-effectiveness, this study utilized vaporized hydrogen peroxide (VHP) generated from sodium percarbonate granules to conduct an anhydrous disinfection test on gastrointestinal endoscopes.

METHODS

The experimental device rapidly converts sodium percarbonate granules into VHP, and performs disinfection experiments on gastrointestinal endoscope models, disposable endoscopes, and various types of reusable gastrointestinal endoscopes. Variables such as the intraluminal flow rate (FR), relative humidity (RH), exposure dosage, and organic burden are used to explore the factors influencing the disinfection of long and narrow lumens with VHP.

RESULTS

The device generates a certain concentration of VHP that can achieve high-level disinfection of endoscope models within 30 minutes. RH, exposure dosage, and organic burden significantly affect the disinfection efficacy of VHP, whereas the intraluminal FR does not significantly impact disinfection efficacy. All ten artificially contaminated disposable endoscopes achieved satisfactory disinfection results. Furthermore, when this device was used to treat various types of reusable endoscopes, the disinfection and sterilization effects were not significantly different from those of automatic endoscope disinfection machines (using peracetic acid disinfectant solution) (P > 0.05), and the economic cost of disinfectant required per endoscope was lower (1.5 China Yuan), with a shorter disinfection time (30 minutes).

CONCLUSION

The methods and results of this study provide a basis for further research on the use of VHP for the disinfection of gastrointestinal endoscopes, as well as for the development of anhydrous disinfection technology for gastrointestinal endoscopes.

Key Words: Gastrointestinal endoscope; Vaporized hydrogen peroxide; Sodium percarbonate granules; Bacillus subtilis; Anhydrous disinfection

Core Tip: This study pioneers an anhydrous disinfection method for gastrointestinal endoscopes using vaporized hydrogen peroxide generated from sodium percarbonate granules. Demonstrating comparable efficacy to traditional liquid disinfectants, the method achieves high-level disinfection within 30 minutes while reducing water use, costs (1.5 China Yuan per cycle), and environmental impact. Key factors-humidity, exposure dosage, and organic burden-significantly influence efficacy, with no adverse effects from flow rate variations. This innovation aligns with green endoscopy goals, offering a sustainable, efficient alternative to resource-intensive reprocessing, and sets a foundation for future anhydrous sterilization technologies.

INTRODUCTION

Gastrointestinal endoscopes are slender and complex medical devices with long lumens. Currently, with the rapid development of endoscopy technology, various types of endoscopes are being used more extensively for the treatment of lesions; therefore, they are classified as semicritical medical devices that must undergo a high-level of disinfection or even sterilization, before reuse to ensure medical safety[1]. Most endoscopy examination institutions, in accordance with medical standards, commonly use disinfectants such as ortho-phthalaldehyde, glutaraldehyde, peracetic acid, chlorine dioxide, acidic oxidizing potential water, ethylene oxide, hydrogen peroxide low-temperature plasma, and low-temperature steam formaldehyde for endoscope disinfection. The large volume of endoscopy examinations and the flow of multiple nonrenewable waste streams result in the extensive use of water resources and the production of a large amount of medical waste, making endoscopes among the top three contributors of medical waste in hospitals[2,3]. Disposable endoscopes can address the issue of cross-infection among endoscopes while also preventing the consumption of large amounts of resources during endoscope reprocessing. However, disposable devices themselves become medical waste after use, and their carbon footprint is 20 times greater than that of reusable endoscopes, which does not align with the current concept of green endoscopy[4,5]. The issue of environmental protection during the endoscopy service process is a significant challenge that must be addressed.

To meet this demand, the aim of this study was to explore a new method of disinfecting endoscopes that completely eliminates liquid disinfectants and is based on solid and gaseous substances. Although ethylene oxide and formaldehyde are also gaseous disinfectants that can achieve sterilization levels, they are highly toxic, require aeration, and significantly extend the sterilization time. Vaporized hydrogen peroxide (VHP) has rapidly developed in the past decade as an efficient disinfectant that is expected to replace ethylene oxide gas for the disinfection and sterilization of endoscopes[6]. Hydrogen peroxide has demonstrated effective antimicrobial activity against a variety of organisms, including bacteria, bacterial spores, fungi, bacilli, and viruses, without producing carcinogenic or toxic residues[7]. Past studies have demonstrated that VHP is superior to hydrogen peroxide solutions in denaturing serum albumin and possesses a stronger disinfecting power than liquid disinfectants. Moreover, the spatial distribution of gaseous disinfectants is more uniform than that of liquid disinfectants, with a stronger diffusion capability, enabling more effective disinfection of complex structures on endoscopes[8,9].

Sodium percarbonate granules are an effective alternative to hydrogen peroxide solutions[10-12], offering greater stability and safety than concentrated hydrogen peroxide solutions. These granules degrade quickly, are environmentally friendly and are considered green disinfectants[13]. On the basis of the above principles, for this study we designed a device that rapidly converts sodium percarbonate granules into VHP for disinfection within the endoscope lumen. We utilized endoscope models, disposable endoscopes, and various types of reusable gastrointestinal endoscopes as research subjects to study the disinfection effects of VHP on endoscopes and to explore a new model for anhydrous disinfection of gastrointestinal endoscopes.

MATERIALS AND METHODS

Solid-gas phase VHP disinfection device

Figure 1 present the perspective and actual views (Figure 1A and B) of the experimental device designed and manufactured in this study, as well as detailed diagrams (Figure 1C-F) of some components. The device consists of four parts: The reaction vessel, heating control module, ultrasonic oscillation module, and flow control module. Sodium percarbonate granules were rapidly converted into VHP under the action of high-temperature heating and ultrasonic vibration. Then the gas was introduced into the endoscope lumen for disinfection through the gas nozzle at the top of the flow control module.

Figure 1 Schematic and photos of the vaporized hydrogen peroxide generation device. A: The perspective view of the experimental device; B: The actual view of the experimental device; C: Reaction vessel; D: Temperature control panel; E: Ultrasonic control panel; F: Flow meter. ¹Gas nozzle; ²Flow meter; ³Reaction vessel; ⁴Ultrasonic generator; ⁵Temperature control panel; ⁶Heating plate; ⁷Vibration plate; ⁸Ultrasonic control panel.

Design of the gastrointestinal endoscope model

To adequately simulate the structure and material of a gastrointestinal endoscope, the endoscope model consisted of a polytetrafluoroethylene (PTFE) tube with an outer diameter of 8 mm, an inner diameter of 6 mm, and a total length of 2000 mm. The endoscope model was cut into four sections at the 50 mm, 1000 mm, and 1950 mm marks, with bacterial carriers inserted at the three cuts to simulate different contamination sites of the endoscope (Figure 2). The PTFE tubes were securely fitted with the bacterial carriers, and all the tubes were subjected to a degreasing process and autoclaved for sterilization before application. The design of the validation test referred to the Evaluation Method of Endoscopic Disinfection Effect (2020 Edition, China) and international organization for standardization (ISO) 22441: 2022 Sterilization of health care products - Low temperature vaporized hydrogen peroxide - Requirements for the development, validation and routine control of a sterilization process for medical devices.

Figure 2 Schematic diagram of the gastrointestinal endoscopy model. BC: Bacterial carrier; VHP: Vaporized hydrogen peroxide.

Bacterial preparation and carrier inoculation

This experiment refers to the Evaluation Method of Endoscopic Disinfection Effect (2020 Edition, China) and the contents of ISO 11138-6, Sterilization of health care products-Biological indicators before Bacillus subtilis (B. subtilis) spores (ATCC 9372) were used as a biological indicator. The diluent was tryptone physiological salt solution, and the culture medium was nutrient agar (9 cm, Beckman Biology). A pipette was used to drop 0.02 mL of spore suspension onto the inner wall of the PTFE tube carrier (outer diameter of 6 mm, inner diameter of 4 mm, and length of 30 mm), which had been defatted and sterilized by autoclaving, after which it was spread evenly. The recovery bacterial count for each carrier ranged from 1 × 10⁶ to 5 × 10⁶ colony-forming units (CFUs). All carriers with spores were placed on plates on a clean workstation for 30 minutes to dry before use. The prepared bacterial carriers were used within 24 hours of inoculation.

Methods

The device was placed inside a disinfection chamber with dimensions of 500 mm × 500 mm × 500 mm. The chamber was equipped with a VHP concentration sensor (HPP271, Vaisala, Finland), temperature and humidity sensors (HMD60Y, Vaisala, Finland), and a negative pressure ventilation pipe to allow for continuous monitoring of the working status of the disinfection device. During disinfection, the sodium percarbonate granules were first placed into the reaction vessel. All parameters of the device were set, the endoscope model or the various channels of the endoscopes were connected, and the heating and ultrasonic vibration modules were turned on. Approximately 5 minutes later, when the VHP concentration in the chamber reached its peak, the timing began. After disinfection was complete, the residues were removed, and disinfection was subsequently performed.

Laboratory experiments: The contaminated carriers were connected to the gas generation device nozzle, the disinfection device was activated, the timing was started after 5 minutes, and disinfection was applied for 10 minutes, 20 minutes, and 30 minutes, respectively. After disinfection, the carriers were sampled and incubated in a 36 ± 1 °C incubator for 72 hours. The results were observed, the viable bacteria were counted, and those bacteria were considered the experimental group. For each exposure time, three carriers were selected for parallel experiments, and each carrier was inoculated into two Petri dishes for cultivation. Additionally, the same contaminated carriers were connected to the gas generation device nozzle, the device was continuously turned off, and after 30 minutes, the carriers were removed for cultivation. Again, the same steps were followed, the viable bacteria were counted, and these bacteria were considered the positive control group. Additionally, two uncontaminated carriers were subjected to similar steps as those in the negative control group. The experiment was repeated three times, the viable bacterial counts (CFU/carrier) for each group were calculated, and the log reduction value was calculated via the formula KL = N₀ - N_X, where N₀ and N_X represent the CFUs recovered from the positive control and disinfected carriers, respectively. The results were considered valid if the positive control group showed bacterial growth, the negative control group showed no bacterial growth, and the experimental group had a log reduction value of ≥ 5.00.

Endoscope model disinfection tests: The endoscope models with contaminated carriers were connected to the nozzle of the device and disinfection began. After disinfection was complete, the carriers were removed from various parts, samples were taken, and the samples were placed in a 36 ± 1 °C incubator for 72 hours for cultivation. The results were observed, and viable bacteria in the experimental group were counted. Additionally, the same endoscope model was taken and connected to the device's nozzle with the disinfection device continuously turned off. After 30 minutes, the carriers were removed, and the same steps were followed for cultivation as mentioned above, with the positive control group considered. Additionally, physiological saline was inoculated onto Petri dishes for 72 hours for cultivation, the results were observed, and viable bacteria were counted as the negative control group. The experiment was repeated three times, and the log reduction values for each group were calculated. The results were considered valid if the positive control group showed bacterial growth, the negative control group showed no bacterial growth, and the experimental group had a log reduction value of ≥ 3.00. Previous research results have indicated that relative humidity (RH), the intraluminal flow rate (FR), the exposure dosage, and the organic burden may be the main factors affecting the effectiveness of gas disinfection[14,15]; therefore, these factors are used as variables to further explore the disinfection parameters of VHPs.

Disposable endoscope disinfection tests: Ten disposable endoscopes (EndoFresh) were selected for disinfection testing. After rigorous cleaning and disinfection, the samples were kept ready for use. A pipette was used to inject a spore suspension equivalent in volume to that of the simulated endoscope into the biopsy channel entrance and the suction channel of the endoscope. The height of the endoscope channels was adjusted to evenly distribute the bacterial mixture within the lumen. The surface of the endoscope was wiped with gauze soaked in the bacterial mixture and placed on a clean workstation for 1 hour before use. Before the disinfection test, prewashing, cleaning, and final rinsing steps were performed for each endoscope. Swab samples were taken from the biopsy port, surface, suction channel, and lumen of each endoscope; these swab samples were then used for culture. After disinfection, samples were taken again from each part, and the total number of colonies ≤ 20 CFU per item was considered valid.

Reusable endoscope disinfection tests: A total of 120 reusable gastrointestinal endoscopes (including 40 gastroscopes, 40 colonoscopes, and 40 duodenoscopes) were selected, and each type of endoscope was randomly assigned into groups. One group was the experimental group, which was disinfected via a VHP disinfection device, and samples were collected for testing after disinfection. After sampling, the experimental group was disinfected again via an automated endoscope reprocessor (AER) to ensure full compliance with the disinfection process. Another group was the control group, which was disinfected with an AER (peracetic acid solution), and samples were collected for testing after disinfection. The experimental group underwent a drying step before disinfection to reduce the impact of residual droplets absorbing VHP by the disinfection effect (Figure 3). Disinfection was considered valid if the total colony count was ≤ 20 CFU per item and no pathogenic bacteria were present; sterilization was achieved if no colonies were detected throughout the endoscope. The disinfection and sterilization effectiveness of the two groups were compared.

Figure 3 Study design and procedures of the reprocessable endoscope disinfection test. VHP: Vaporized hydrogen peroxide; AER: Automated endoscope reprocessor.

Statistical analysis

SPSS statistics software (version 26.0) was used for analysis of variance and χ² tests of the experimental data. P values of less than 0.05 were considered statistically significant.

RESULTS

Laboratory disinfection efficacy

Seventy-five g of sodium percarbonate granules were added to the device, and the contaminated carriers were disinfected for 10 minutes, 20 minutes, or 30 minutes. The results, as shown in Table 1, indicate that when the disinfection time is 30 minutes, the log reductions for all carriers are > 5.00. The positive control group recovered an average colony count of 4.5-4.8 × 10⁶ CFU, and no colonies grew in the petri dishes of the negative control group, demonstrating that the VHP produced by 75 g of sodium percarbonate granules can achieve a high-level disinfection (HLD) effect on the B. subtilis spores on the carriers within 30 minutes.

Table 1 Laboratory disinfection efficacy of vaporized hydrogen peroxide.

Disinfection time (minutes)	Total	Unqualified	Qualified	Average CFUs of the positive control group (CFU/bacterial carrier)
10	8	8	0	4.8 × 106
20	8	2	6	4.5 × 106
30	8	0	8	4.7 × 106

CFU: Colony-forming unit.

Endoscope model disinfection tests

Disinfection efficiencies of VHP with various RHs: Figure 4A and B show the log reduction of spores on bacterial carriers treated with 90 mg/L VHP for 30 minutes with an FR of 2.2 L/minutes and various RHs (60%-90%). In general, the disinfection efficiency of VHP for bacterial carriers at the same position increased as the RH increased, which was more pronounced at the outlet. The log reductions of the contaminated carriers at different positions were all > 3.00.

Figure 4 Log reductions of spores on bacterial carriers in the testing devices treated with various relative humidities (60%-90%), exposure dosage (24-45 mg/L/hour), relative humidities (0.8-2.2 L/minute), and organic burdens. A and B: Log reductions of spores by vaporized hydrogen peroxide (VHP) under various relative humidities (RHs) (60%-90%); C and D: Log reductions of spores by VHP under various exposure dosage (24-45 mg/L/hour); E and F: Log reductions of spores by VHP under various FRs (0.8-2.2 L/minute); G and H: Log reductions of spores by VHP under various organic burdens. ^aP < 0.05; ^bP < 0.01; ^cP < 0.001; NS: Not significant; BC: Bacterial carrier; BSA: Bovine serum albumin.

Disinfection efficiencies of VHP at various exposure dosages: As shown in Table 2, different exposure dosages were administered. Figure 4C and D show the disinfection efficiency of VHP in the inactivation of spores on bacterial carriers with various exposure dosages (24-45 mg/L/hour), 80% RH and 2.2 L/minutes FR. The results indicate that the disinfection efficiency of VHP for bacterial carriers at the same position increased as the exposure dosage increased. The log reductions of the contaminated carriers at different positions were all > 3.00.

Table 2 Vaporized hydrogen peroxide treatment dosages with different concentrations and disinfection times.

Concentration of VHP (mg/L)	Disinfection time (minute)	Exposure dosage (mg/L/hour)
72	20	24
90	20	30
72	30	36
90	30	45

VHP: Vaporized hydrogen peroxide.

Disinfection efficiencies of VHP with various intraluminal FRs: The log reductions of spores on bacterial carriers following the 30 minutes treatment with 90 mg/L VHP, 80% RH, and various FRs (0.8-2.2 L/minutes) are shown in Figure 4E and F. In general, the intraluminal FR did not significantly affect the disinfection efficacy of VHP (P > 0.05). The log reductions of the contaminated carriers at different positions were all > 3.00.

Disinfection efficiencies of VHP with various organic burden: Figure 4G and H show the log reductions of spores on bacterial carriers treated with 90 mg/L VHP for 30 minutes with 80% RH, 2.2 L/minutes FR and various organic burdens. The results show that the organic burden has a significant effect on the disinfection efficacy of VHP, which is reflected mainly in the bacterial carrier at the outlet. Tryptone soy broth (TSB) has little effect on gas disinfection, but higher concentrations of bovine serum albumin (BSA) can reduce the disinfection effect of VHP. The log reductions of the contaminated carriers at different positions were all > 3.00.

Disposable endoscope disinfection tests

Table 3 presents the results of disinfecting disposable endoscopes with VHP. After the predisinfection cleaning steps, a small amount of microbial load still existed in various parts of the endoscope. No viable bacteria were detected in any parts of the disposable endoscopes following the 30 minutes treatment with 90 mg/L VHP, 90% RH, and 2.2 L/minutes FR.

Table 3 Numbers of colonies counted from each sampling location of the disposable endoscopes before and after disinfection via vaporized hydrogen peroxide.

No.	Number of colonies (CFU/item)
	Biopsy channel		Biopsy valve		Endoscope surface		Suction channel
	BD	AD	BD	AD	BD	AD	BD	AD
1	10	0	0	0	10	0	19	0
2	40	0	0	0	0	0	24	0
3	140	0	38	0	7	0	6	0
4	30	0	12	0	11	0	0	0
5	10	0	12	0	0	0	0	0
6	20	0	0	0	0	0	0	0
7	10	0	0	0	0	0	0	0
8	100	0	18	0	42	0	102	0
9	20	0	25	0	0	0	58	0
10	80	0	12	0	18	0	7	0

CFU: Colony-forming unit; BD: Before disinfection; AD: After disinfection.

Verification of the effectiveness of disinfecting reusable endoscopes with the experimental prototype

Figure 5 illustrates the application scenario of the prototype for disinfecting reusable endoscopes. Tables 4 and 5 compare the HLD and sterilization effects, respectively, of the two methods on gastrointestinal endoscopes. The results indicate that the prototype can essentially achieve the same level of endoscope treatment capability as an AER, with no significant difference in the effects of HLD or sterilization (P > 0.05). Figure 6 shows the comparison of the presence of colonies at different locations of the gastrointestinal endoscopes after treatment by the two reprocessing methods, which revealed no significant difference between the two methods. Moreover, 11 gastrointestinal endoscopes used by patients with positive serology for hepatitis B surface antigen (HBSAg), anti-hepatitis C virus (HCV) antibodies, and TP-Ab were selected for the experiment. After disinfection with the prototype, the abovementioned endoscopes were negative for HBsAg, anti-HCV antibodies, and TP-Ab.

Figure 5 Application scenarios of the experimental device. A: The endoscope's Suction valve, water valve and air valve are connected to the disinfection device; B: The endoscope's biopsy valve is connected to the disinfection device; C: The endoscope to be disinfected is placed on the tray of the disinfection device; D: The endoscope is undergoing anhydrous disinfection.

Figure 6 Comparative forest plot of colony detection at various positions of the endoscope after infection. VHP: Vaporized hydrogen peroxide; AER: Automated endoscope reprocessor.

Table 4 Comparison of the high-level disinfection effects of the two methods on gastrointestinal endoscopes, n (%).

Group	Gastroscope (n = 40)	Colonoscopy (n = 40)	Duodenoscopy (n = 40)	All endoscopes (n = 120)
Experimental group	19 (95)	18 (90)	18 (90)	55 (91.6)
Control group	20 (100)	20 (100)	20 (100)	60 (100)
χ2	0.000	0.526	0.526	3.339
P value	1.000	0.468	0.468	0.068

Table 5 Comparison of the sterilization effects of the two methods on gastrointestinal endoscopes, n (%).

Group	Gastroscope (n = 40)	Colonoscopy (n = 40)	Duodenoscopy (n = 40)	All endoscopes (n = 120)
Experimental group	15 (75)	10 (50)	10 (50)	35 (58.3)
Control group	11 (55)	13 (65)	13 (65)	37 (61.7)
χ2	1.758	0.921	0.921	0.198
P value	0.185	0.337	0.337	0.656

DISCUSSION

Despite continuous innovations in the types and methods of disinfectants, there are still numerous reports of endoscope-related infection incidents globally each year[16,17]. Current disinfection methods consume a considerable amount of water resources and produce a large amount of waste. VHP is a highly efficient, green disinfectant that has been utilized in various fields. However, hydrogen peroxide solutions are very susceptible to decomposition during long-term storage and transportation, light exposure, stirring, and heating, which all accelerate the rate of decomposition[18,19]. Sodium percarbonate has been used as a solid alternative to hydrogen peroxide solutions, offering advantages such as nontoxicity, chemical stability, and environmental friendliness[20]. We designed and tested a prototype device for disinfecting gastrointestinal endoscopes via VHP, with sodium percarbonate granules as the raw material, which required no water involvement in the entire disinfection process. The residues after disinfection are easy to handle and are relatively harmless to the environment.

Comparison of the VHP method with an AER

Compared with an AER device, the prototype device can treat any type of gastrointestinal endoscope in just 30 minutes via VHP produced from 150 g of sodium percarbonate granules, with disinfection and sterilization effects showing no significant difference. The disinfection time is shorter than that of an AER or peracetic acid solution (37 minutes for gastroscopes and colonoscopes and 68 minutes for duodenoscopes). The cost of the disinfectant (sodium percarbonate granules) is only 1.5 China Yuan (CNY) per endoscope, which is significantly lower than the 28.7 CNY per endoscope for peracetic acid disinfectant solution, and the solid granules require much less storage space than do the liquid disinfectants. Additionally, the prototype device produces almost no detectable irritating odors during the disinfection process. Overall, this VHP disinfection device is cost effective, environmentally friendly, and harmless to humans, and the disinfection concentration can be monitored in real time.

Notably, this anhydrous disinfection method requires two drying processes, which may increase the workload of the disinfection staff.

Biological indicators

Biological indicators are microorganisms that possess greater resistance than the microorganisms killed on medical devices[6]. Among the different types of microorganisms, spores of gram-positive bacteria are the most resistant to chemical disinfectants. Therefore, if a disinfectant is able to disinfect spores of gram-positive bacteria to a certain degree, it can theoretically inactivate all other pathogens as well[21]. B. subtilis spores have been widely used as biological indicators for the disinfection of various gaseous disinfectants[22]. Therefore, it was selected as the sole biological indicator bacterium in this study.

Factors influencing the disinfection efficacy of VHP

This study revealed that the exposure dose, RH, and organic burden can affect the killing effect of VHP on spores. The higher the exposure dose is, the better the disinfection effect of VHP. On the basis of this result, the concentration of VHP can be increased to achieve faster disinfection. With respect to the impact of RH on the disinfection effect of VHP, Beatriz from Germany conducted relevant experiments[23], whose study revealed that under relatively low VHP concentrations (≤ 400 mg/L), relatively high RH would increase the disinfection level. Additionally, higher humidity conditions cause water molecules to expand the volume of spores, and the increased surface area of the spores increases the susceptibility of the spore wall to breakthrough by VHP[24,25]. Similar results were obtained in this study, where the killing effect on spores increased with increasing RH at a VHP concentration of 90 mg/L. Therefore, increasing the environmental RH may be beneficial for improving disinfection efficacy, reducing the amount of disinfectant, lowering disinfection costs, and minimizing the potential damage of VHP to endoscopes.

The presence of organic matter on the surface of endoscopes can hinder contact between disinfectants and microorganisms, reduce the killing effect, and facilitate the formation of biofilms, greatly increasing the risk of endoscope-related infections[26]. In this study, 3% BSA significantly reduced the disinfection effect of VHP compared with 0.3% BSA, whereas TSB did not have a significant interfering effect. This fully demonstrates the importance of cleaning to remove a large organic load before disinfection[27].

Furthermore, the results of this study show that the variation in FRs in the lumen did not significantly affect the killing effect of VHP on spores. Some studies have indicated that VHP has a greater ability to penetrate three-dimensional structures composed of proteins, lipids, and polysaccharides than hydrogen peroxide, and VHP is more capable of damaging the spore wall and subsequently the DNA within spores[7,28,29]. The variation in the FR within the range of 0.8-2.2 L/minutes may not be sufficient to affect the destruction of spores by VHP, and further research is needed to determine the specific threshold that would make a difference.

Although this study confirms the efficacy of hydrogen peroxide gas in disinfecting the lumen of digestive endoscopes, its penetration is still the focus of international controversy. The presence of hydrogen peroxide gas in the slender lumen may be due to high diffusion resistance and uneven gas distribution, resulting in insufficient local concentration, thus affecting disinfection efficacy. This limitation is confirmed by the significantly lower number of log spores killed at the exit of the simulated endoscope model than at the entry point in this experiment. The following improvement directions can be considered: One is to optimize the aerodynamic mode, using pulsed gas flow instead of continuous gas flow, enhancing the penetration depth of gas in the lumen through pressure fluctuations, and integrating multidirectional nozzles in the device to inject gas bidirectionally from the biopsy port and suction port of the endoscope to reduce the "dead space" effect; the other is to install a hydrogen peroxide concentration sensor at the end of the lumen, dynamically adjusting the gas flow and exposure time to ensure that the minimum effective concentration is up to the standard during the whole process; and the third is collaborative technology integration, which uses the cavitation effect of low-frequency ultrasound (20-40 kHz) to destroy the biofilm structure, improve the contact efficiency between gas and microorganisms, and introduce plasma activation technology to stimulate hydrogen peroxide gas to generate reactive oxygen species, enhancing the killing ability of deep pollution.

Limitations of this study

Although this test verified the effects of RH, exposure dosage, and organic burden on the disinfection of VHP, the optimal operating parameters of the device were not further investigated to explore the disinfection potential of VHP. The test device could disinfect only one endoscope at a time, and its effect on the simultaneous disinfection of multiple endoscopes was not investigated. The potential damage of VHP to endoscopic equipment, which is closely related to the disinfection concentration and time, was not further investigated.

CONCLUSION

The experimental results indicate that treating gastrointestinal endoscopes with VHP generated from sodium percarbonate granules can essentially achieve the disinfection effect of an AER and peracetic acid mixture, significantly reducing the cost of disinfectants. Moreover, the entire disinfection process greatly reduces the use of water. By adjusting parameters such as gas concentration and RH, the disinfection time can be greatly shortened; this provides valuable ideas for achieving rapid and anhydrous disinfection, as well as realizing the concept of green endoscopy.

ACKNOWLEDGEMENTS

We sincerely thank the peer reviewers for their comprehensive and constructive suggestions on this manuscript.