Under the dynamic environment of normal diagnosis and treatment in the bronchoscope room, the study of the removal efficiency of the new air purifier on microbial aerosols


 Background

The SARS-CoV-2 can spread through droplets, aerosols, etc. In the case of a severe outbreak of the SARS-CoV-2, the use of new air purifiers in work and living places has a certain effect on reducing the spread of the SARS-CoV-2. There are abundant microbial aerosols in the indoor medical environment. The innovation of this experiment lies in the use of long-term, large-volume sampling methods under the multi-factor dynamic conditions of normal diagnosis and treatment in the bronchoscope room, and the use of two microbial detection methods at the same time to study the removal efficiency of the new air purifier on microbial aerosols ; The innovation of the new air purifier lies in outdoor fresh air and steady-state displacement flow technology.
Methods

In this experiment, the test group and the control group were set up. Gelatin filtration membrane and PTFE filtration membrane were used to sample the microbial aerosols in the bronchoscope room. Long time (39.5h) and large sampling volume (70590L) was used. A total of 16 days of pure working time sampling was carried out for a period of 1 month. The collected specimens were tested by two methods: next-generation sequencing (mNGS) and microbial culture identification. The researcher retrieved and recorded the microbiological test results of related patients, and compared them with the results of this experiment.
Results

The result of next-generation sequencing (mNGS): The total purification efficiency was 88.0%. Microbial culture counting and identification results: the total purification efficiency is 87.5%. The results are statistically significant. There is a certain correlation between the experimental results and the clinical microbiological test results of patients.
Conclusions

1. The new type of air purifier has a good effect on the removal of microbial aerosols in the bronchoscope room; 2. A variety of microorganisms involved in the experiment can be transmitted through aerosols.
Discussion

The new air purifier has a total removal efficiency of more than 85% of microorganisms under the dynamic environment of the hospital's normal diagnosis and treatment, and the purification efficiency of a single microorganism ranges 50%-100%. Such removal efficiency may have a positive effect for the control of the SARS-CoV-2 epidemic.


Background
The SARS-CoV-2 can spread through droplets, aerosols, etc. In the case of a severe outbreak of the SARS-CoV-2, the use of new air puri ers in work and living places has a certain effect on reducing the spread of the SARS-CoV-2. There are abundant microbial aerosols in the indoor medical environment. The innovation of this experiment lies in the use of long-term, large-volume sampling methods under the multi-factor dynamic conditions of normal diagnosis and treatment in the bronchoscope room, and the use of two microbial detection methods at the same time to study the removal e ciency of the new air puri er on microbial aerosols ; The innovation of the new air puri er lies in outdoor fresh air and steadystate displacement ow technology.

Methods
In this experiment, the test group and the control group were set up. Gelatin ltration membrane and PTFE ltration membrane were used to sample the microbial aerosols in the bronchoscope room. Long time (39.5h) and large sampling volume (70590L) was used. A total of 16 days of pure working time sampling was carried out for a period of 1 month. The collected specimens were tested by two methods: nextgeneration sequencing (mNGS) and microbial culture identi cation. The researcher retrieved and recorded the microbiological test results of related patients, and compared them with the results of this experiment.

Results
The result of next-generation sequencing (mNGS): The total puri cation e ciency was 88.0%. Microbial culture counting and identi cation results: the total puri cation e ciency is 87.5%. The results are statistically signi cant. There is a certain correlation between the experimental results and the clinical microbiological test results of patients. Conclusions 1. The new type of air puri er has a good effect on the removal of microbial aerosols in the bronchoscope room; 2. A variety of microorganisms involved in the experiment can be transmitted through aerosols.

Discussion
The new air puri er has a total removal e ciency of more than 85% of microorganisms under the dynamic environment of the hospital's normal diagnosis and treatment, and the puri cation e ciency of a single microorganism ranges 50%-100%. Such removal e ciency may have a positive effect for the control of the SARS-CoV-2 epidemic.

Highlights
The innovation of this experiment lies in the use of long-term, large-volume sampling methods under the multi-factor dynamic conditions of normal diagnosis and treatment in the bronchoscope room, and the use of two microbial detection methods at the same time to study the removal e ciency of the new air puri er on microbial aerosols ; The innovation of the new air puri er lies in outdoor fresh air and steadystate displacement ow technology.
Background A large number of liquid particles are produced in human production and life, and the particle size of this part of the liquid particles is mostly between 0.001 µm and 100 µm. Generally, the particle size: 5µm is the dividing line. The particles larger than 5µm are droplets, and the particles smaller than 5µm are aerosols [1] . Particles containing microorganisms are called microbial aerosols. The microbial aerosols collected in this experiment are a kind of small and medium particles. In recent years, the SARS-CoV-2 raging around the world can be spread through droplets, aerosols, etc [2] . The droplet is affected by gravity and has a short diffusion distance. It is a kind of short-distance transmission between people, and aerosols can remain suspended for a long time [3] , so microbial aerosols are an important cause of the transmission of indoor infectious diseases.
Because of the higher risk of medical staff being exposed to indoor microbial aerosols [4][5] . The risk ratio for health care workers to acquire viral or bacterial infections is 2.5 [6] . The staff in the endoscopy room are at increased risk of contracting the SARS-CoV-2 [7] . Humans have long discovered that many microorganisms can be transmitted by droplets, but aerosol transmission is still unclear. Indoor microbial aerosol has an important impact on the the spread of established infectious pathogens such as the known SARS-CoV-2 [8] , Mycobacterium tuberculosis, measles virus, varicella-zoster virus [9][10] , hand-footmouth disease virus [11] , Ebola virus and Middle East Respiratory Syndrome virus [12] . In addition, indoor microbial aerosols are important in different medical places such as operating room [13] , intensive care room [2,14] , nasopharyngeal swab collection place [15] , endoscopy room [16] , Stomatology [20] , Otorhinolaryngology [17] , Gastroenterology [18] and Ophthalmology [19] , etc. Microbial aerosols also have an important impact on medical staff and patients. The control of indoor microbial aerosols can also reduce the hospital infection rate of patients. The location of the sampling point designed in this experiment decides that the sampling membranes can only collect aerosols without droplets. Therefore, the experimental results can also con rm that the relevant microorganisms are transmitted through aerosols.
Some studies [21][22] directly take samples from the lters of air conditioners or puri ers for microbiological testing, which indirectly con rms the purifying effect of the lter. However, the microorganisms on the lter will multiply, die or decompose, so the method above cannot directly re ect the microbial aerosols. Some scholars [23][24][25][26][27] have con rmed that air puri ers can effectively reduce the concentration of allergens in indoor air, thereby improving the clinical manifestations of patients with allergic rhinitis, and signi cantly reducing the drug needs. Some scholars [28] have proved that the air puri er has the effect of reducing the total colony number of the culture medium through the method of air sampling and fungus culture in the medium, but it has not been tested for bacterial species, and the puri cation of each microorganism cannot be seen directly. Some scholars [29][30] use aerosol generators to arti cially make certain virus and bacterial solutions into aerosols. Under the ideal conditions of a closed experimental chamber, they have con rmed that air puri ers have a certain puri cation effect on aerosols of speci c types of microorganisms. It can intuitively re ect the puri cation effect, but it is not an evaluation of the puri cation effect on the microorganisms that actually exist under the dynamic environmental conditions of the normal diagnosis and treatment of the hospital. In animal experiments, some scholars [31] have proved that air puri ers are effective in reducing the pathogenicity of certain viruses to animals by detecting the infection rate of animals to certain viruses, but they cannot directly re ect the puri cation of air puri ers on microbial aerosols.
The new type of air puri er used in this experiment is Aoxiang® Steady-State Displacement Flow Clean and Disinfection System, and the puri cation factor is steady-state displacement ow eld and highe ciency air ltration technology. The new air puri er uses an energy-saving and e cient air cleaning technology: steady-state displacement ow technology. In the indoor environment between the air outlet and the air inlet, a "vector ow" one-way and propelling air ow is established, so that the particulate matter is removed with the minimum amount of diffusion. This technology can establish a push-type displacement ow eld to form an air isolation barrier in the controlled area. It is a kind of purely physical epidemic prevention technology and may play a positive role in the prevention and control of epidemics in public places, including the medical environment.

Materials And Methods
This experiment is used in the dynamic environment of clinical practical work to actually investigate the puri cation effect of air puri ers on indoor microbial aerosols. In order to solve the multi-factor problems of uncertain number of patients, uncertain types of diseases, uncertain time of treatment, uncertain species of the collected microorganism, su cient air collection to reach the lower limit of the detection method, and comparison of the puri cation e ciency of a single microorganism, the researchers used a long time ( 39.5h), large sampling capacity (70590L) method. The collection time of the similar research ranges from 15min-2h, and the collection volume ranges 50-2000L [32][33][34][35][36] . In this experiment, a total of 16 days of pure working time sampling was carried out for a period of 1 month. The amount of air collected is large enough to represent the average puri cation e ciency of the microbial aerosol in the bronchoscope room, which is more statistically signi cant.

Experimental equipment and experimental materials
New air puri er (China Aoxiang), Circulating water vacuum pump (China Lichen), 37mm lter membrane sampling clip (USA SKC), Gelatin lter membrane (Germany Sartorius), PTFE lter membrane (China Chuangwei) 2.1.1.The new type of air puri er: The new type of air puri er used in this experiment is Aoxiang® Steady-State Displacement Flow Clean and Disinfection System: Model AXY1, the batch number is 20201120004, and the puri cation factor is steady-state displacement ow eld and high-e ciency air ltration technology.

The lters:
The gelatin lter membrane used in this experiment has a positive effect on maintaining microbial activity and has been widely used in air microbial sampling.

Experimental conditions:
Temperature ranges 23-26℃, humidity ranges 40-65%; the experimental conditions of the unpuri ed group and the puri ed group are the same. (1) Dissolve the sampling membranes of No. 1, 3, 4, and 5 after sampling in 4ml of sample storage solution dedicated to mNGS, and place the dissolving mixture in a 37°C water bath for 7 minutes, and mark as the unpuri ed group. Dissolve the sampling membranes A, C, D, and E after sampling in 4ml of the second-generation sequencing (mNGS) special specimen storage solution, place them in a 37°C water bath for 7 minutes, and mark them as the puri ed group. The sample solution obtained in this step is tested by second-generation sequencing (mNGS).
(2) Dissolve the No. 2 sampling membrane in 2ml of normal saline, place it in a 37°C water bath for 7 minutes, and mark it as the unpuri ed group. Dissolve the B sampling membrane in 2ml of normal saline, place it in a 37°C water bath for 7 minutes, and mark it as the puri ed group. Extract 1 mL of each specimen, and inoculate it on Agar medium and Sabouraud medium respectively by streaking on the plate, and then cultivate the colonies. Culture conditions: Agar medium 35°C for 48 hours, Sabouraud medium 26°C for 72 hours.
2.8. The situation of patients undergoing bronchoscopy during the sampling period in the bronchoscope room: Puri cation e ciency = (copy number of unpuri ed group-copy number of puri ed group)/copy number of unpuri ed group = 88.0%.
The researchers used SPSS statistics 26 to perform non-parametric tests, and the statistical results are as follows: At the level of α=0.05, P<0.05, the researcher can think that there is a statistical difference in the copy number of next-generation sequencing (mNGS) of different microorganisms between the unpuri ed group and the puri ed group.

Bacteria and fungi culture and identi cation results (1) Colony count result
The comparison of the total number of colonies between the puri ed group and the unpuri ed group is as follows: Puri cation e ciency = (the number of colonies in the unpuri ed group-the number of colonies in the puri ed group) / the number of colonies in the unpuri ed group = 87.5% (2) Strain identi cation results The researchers identi ed the dominant colonies in the culture medium. The results are as follows: Among them, Aspergillus avus is a special case, the discussion part will be analyzed separately. The puri cation e ciency of the remaining 5 microorganisms are: Aspergillus fumigatus: 87.5%, Aspergillus niger: 100%, Klebsiella pneumoniae: 100%, Micrococcus luteus: 100%, Bacillus subtilis: 50%.
The researchers performed non-parametric tests on the remaining 5 microorganisms using SPSS statistics 26. The statistical results are as follows: At the level of α=0.05, P<0.05, the researcher can think that there is a statistical difference in the number of colonies of different types of microorganisms between the unpuri ed group and the puri ed group.

Case investigation
The researchers retrieved the information of patients who underwent bronchoscopy during the sampling period and recorded their clinical microbiological test results such as sputum culture, blood culture, respiratory pathogen antibody detection, alveolar lavage uid culture, and second-generation sequencing of alveolar lavage uid ( mNGS) and so on. The researchers found that during the sampling period of the unpuri ed group, the corresponding microorganisms that were consistent with the experimental results were found as follows: Klebsiella pneumoniae, Actinomyces endostei, Staphylococcus capitis, Gardnerella vaginalis, Pseudomonas aeruginosa Spp., Stenotrophomonas maltophilia, and Fusarium. During the sampling period of the puri ed group, the corresponding bacteria or fungi that were consistent with the experimental results were found as follows: Aspergillus avus.

Discussion
Experiments have con rmed that after puri cation by the new type of puri er, the total number of copies and colonies in the bronchoscope room has been greatly reduced, and the total puri cation e ciency is 87.5%-88%. Moreover, individual strains identi ed by mNGS and microbial culture also have different degrees of declining, with a puri cation e ciency of 50%-100%, and most of the strains have a puri cation e ciency of 100%. It can be seen that in the dynamic environment of normal diagnosis and treatment in the bronchoscope room, the new type of puri er has a good puri cation e ciency for indoor microbial aerosols. The long-term, large-volume sampling method used in this experiment conforms to the regulations of statistics.
After puri cation, the total amounts and types of most microorganisms are greatly reduced. However, there is a special case: Aspergillus avus. The researchers conducted a case search and found that the only patient whose clinical microbiological examination results were positive for Aspergillus avus entered the bronchoscopy room during the sampling period of the puri ed group and was examined by bronchoscopy. Therefore, the aerosols of Aspergillus avus are produced in the puri ced group and collected by the sampling membranes. The sampling membranes sent for microbial culture and strain identi cation is the 2/B one, which is 2.5-3.5m away from the patient and is the closest. Due to the application of the puri er's steady-state replacement ow, the indoor air ow is slow, and its normal air ow cannot be detected by the human body. After the aerosol produced by the patient, it has not been eliminated by the puri er immediately, and it has been collected by the sampling membrane. The reason for the unexistence of Aspergillus avus in the mNGS results is that the sampling positions of the membranes submitted to mNGS are far away from the patients, and the aerosols produced by the patients are not collected by the sampling membranes in time. The above is the reason that the number of colonies of Aspergillus avus in the puri ed group is more than that in the unpuri ed group. This situation is inevitable in the dynamic environment of the current experiment. Even so, the overall microbial removal rate of the experiment was not affected. This experiment uses two methods for microbial detection, and the experimental results are surprisingly similar. This can prove that the new type of puri er has a relatively stable puri cation e ciency for indoor microbial aerosols in a dynamic diagnosis and treatment environment, which is 87.5%-88%.
The puri cation time of the experiment was set to 40 min. The new air puri er can have a relatively obvious particle materials puri cation effect when it is opened for about 10 minutes, which has been con rmed in the airtight experimental chamber. However, in the normal diagnosis and treatment environment of the bronchoscope room, a more stable particle materials puri cation effect can be achieved 40 minutes after the puri er is turned on. Therefore, the puri cation time set in this experiment is 40 minutes. Compared with traditional disinfection methods, the new type of puri er can be used in a medical environment at any time. The new type of puri er is equipped with an upwind side and a downwind side, which can protect the safety of medical staff and patients to the greatest extent, and can also push the indoor particulate matter down to the greatest extent, keeping it away from the mouth and nose of medical staff and patients, and reduce the chance of infection in hospital.
The current SARS-CoV-2 pandemic, many countries are currently experiencing an epidemic of the novel coronavirus, causing serious casualties and economic losses. Many outbreaks of epidemics are closely related to the indoor environment. Previous studies have agreed that the infection of the endoscopy room is related to the cross-infection of endoscopic equipment [37] . But based on the current sampling results of microbial aerosols, researchers have found that the infection of the endoscopy room is also related to microbial aerosols. So further research are to be done. The new type of air puri er involved in this experiment has a removal e ciency of approximately 85% for microorganisms under the dynamic conditions of the hospital's normal diagnosis and treatment. Such removal e ciency may have a positive effect on the control of the epidemic.

Declarations
Ethics approval and consent to participate( Human Ethics, Animal Ethics or Plant Ethics) Not applicable.

Consent for publication
The Author con rms: that the work described has not been published before; that it is not under consideration for publication elsewhere; that its publication has been approved by all co-authors, if any; That its publication has been approved by the responsible authorities at the institution where the work is carried out.

Availability of data and material
Not applicable.

Competing interests
The authors have no con icts of interest or nancial relationships impacting this manuscript.

Fundings
All funding for this study was supported by the Institute of Respiratory Diseases, the Second Hospital of Hebei Medical University.
Authors' contributions Statistics results of NGS test Results of microbial culture and identi cation test Statistic results of microbial culture and identi cation test Supplementary Files