Evaluation Of Air Disinfection Effect Of COVID-19 Dedicated CT Machine Room

In this paper, three air disinfection methods, UV disinfection lamp, plasma air circulation disinfector, and UV disinfection lamp combined with plasma air circulation disinfector, were used to disinfect the air in the CT room dedicated to COVID-19. The natural sedimentation method was applied to collect samples and evaluate the disinfection effect of the 3 methods.

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1 Materials and Methods

1. Test Object
2. Instruments and equipment
3. Disinfection methods
4. Sampling methods
5. Observation and evaluation index
6. Statistical methods

2 Results

3 Discussion

1. Advantages and disadvantages of air disinfection methods
2. Selection of machine room characteristics and disinfection effects
3. Quality control measures for the disinfection of dedicated CT rooms

4 Conclusion

Multilayer spiral CT scans are the most intuitive way to diagnose and screen for COVID-19. How to smoothly carry out CT examinations in the radiology department, eliminate cross-infection and ensure the safety of doctors and patients has become a common research problem among medical staff. On January 23, 2020, the radiology department of a hospital in China set up a special CT room for COVID-19 in conjunction with the fever clinic and conducted an experimental evaluation study on the air disinfection method of the special CT room.

1 Materials and Methods

1) Test Object

Definition As a 128-layer spiral CT (Siemens, Germany) examination room with an area of about 45 m², the airborne bacterial colony count in the room was used as the test object.

2) Instruments and equipment

UVC germicidal lamp (UVCA Group); SKW-DLX-G150 plasma air disinfector (UVCA Group). Model 3111 CO2 constant temperature incubator (Thermo Scientific, USA).

3) Disinfection methods

The air in the CT room was disinfected using three disinfection methods: UV disinfection lamp, plasma air circulation disinfector, and UV disinfection lamp combined with plasma air disinfector, and samples were collected three times a day.

(1) UV disinfection lamp: according to the area of the machine room, a 30 W straight tube UV disinfection lamp was installed, with the lamp about 2 m from the ground. The UV disinfection lamp was turned on every 8 h when the CT examination was finished and the machine room was unoccupied, and the lamp was turned off after 5-7 min and timed off for 60 min, and left for 10 min before the medical staff entered the machine room for sampling.

(2) Plasma air disinfection machine: use plasma air disinfection machine, turn on the disinfection machine every 8 h when the CT examination is over and the machine room is unoccupied, disinfect the machine with an average circulating air volume of ≥1,000 m³/h for 60 min and then turn it off, and let it stand for 10 min before the medical staff enters the machine room for sampling.

(3) UV disinfection lamp combined with plasma air disinfection machine: plasma air disinfection machine with an average circulating air volume ≥ 1 000 m³/h, 24 h full day on, at the end of the inspection, the machine room when no one turns on the UV disinfection lamp every 8 h, the lamp is on for 10 min after timing 60 min off, and turn off the plasma air disinfection machine, rest for 10 min after medical personnel enters the machine room sampling.

4) Sampling methods

(1) Sampling time: all were disinfected for 60 min and rested for 10 min for sampling 3 times a day, respectively.

(2) Specimen collection: 5-point placement method was used, and nutrient agar plates with a diameter of 9 mm were collected by sedimentation method; the lid was opened during collection and snapped The plates were exposed for 15 min, and then sent for examination immediately.

(3) Culture method: The collected specimens were incubated at 36 ℃ ± 1 ℃ for 48 h. The total bacterial count (cfu/m³) = 50000 N(A × T) was calculated using the formula, where A is the plate area (m²), T is the plate exposure time, and N is the average colony count.

5) Observation and evaluation index

The disinfection effect of the air in the machine room was compared with the above three air disinfection methods, and the bacterial colony count ≤ 4 cfu/(dish-15 min) was qualified.

6) Statistical methods

SPSS22.0 statistical software was used to analyze the data results, and the mean±standard deviation (x±s) was used for measurement data, and t-test was used for independent samples.

2 Results

The difference between the three disinfection methods before and after disinfection was statistically significant ( F=509.0, P<0.05 ); the best disinfection effect was judged to be that of the UV disinfection lamp combined with the plasma air disinfector, as shown in Table 1.

3 Discussion

1) Advantages and disadvantages of air disinfection methods

For 2019-nCoV, which is sensitive to UV light and heat, a UV light for 30 min or 56 ℃ for 30 min can inactivate it. In addition, commonly used disinfectants such as 75% ethanol, iodophor, medium-acting quaternary ammonium salts, chlorine-containing, and peroxide-containing chemical disinfectants can effectively kill 2019-nCoV within the specified time. The main routes of transmission of 2019-nCoV are droplet transmission and contact transmission, and aerosol transmission, although to be further tested, is sufficient to attract attention. Focusing on air disinfection in the hospital environment is an effective means of interrupting droplet and aerosol transmission. According to current reports, the air disinfection methods that can be applied during the 2019-nCoV outbreak mostly use spraying, UV disinfection, and ventilation methods. However, given the construction of CT rooms and the special characteristics of the machines and equipment, these methods all have limitations.

(1) Spray method: It is the most widely used air disinfection method, which generally uses 500 mg/L active chlorine disinfection solution and disinfects by 10 ml/m³ sprays. However, a CT machine is a device composed of many precision electronic components, the temperature and relative humidity of the machine room need to be maintained at 18-22 ℃ and 40%-60% relative constant state. The spray method will change this state, in addition to the liquid leakage of the spray method may cause damage to electrical equipment and corrosion of precision electronic components. There are reports that when the spray method is used, the machine needs to be turned off and covered with plastic film before disinfection, but cross-infection may occur when the plastic film is removed and placed, and multiple switching of the machine will accelerate the loss of the machine.

(2) UV disinfection method: It is the use of a wavelength range of 200 ~ 275 nm C-wave ultraviolet radiation, its sterilization ability, the effectiveness of stability. However, the UVC disinfection method must be carried out when no one is around, and the arrival of patients is usually indefinite, and the disinfection effect will also be reduced over time and the movement of personnel. In addition, maintenance engineers have pointed out that the ozone released can interfere with certain electronic components, which may cause damage to the equipment and affect image quality, and frequent use will accelerate the aging of the CT machine casing and shorten its service life. Currently, many literature reports and expert consensus suggest that UV is sensitive to 2019-nCoV, has a good inactivation effect, and is one of the air disinfection methods that must be used for this outbreak, for which UV disinfection lamps were urgently added to each machine room and controlled experiments were conducted for their disinfection effects.

(3) Ventilation method: is the easier air disinfection method, but the dust-free needs of CT machines make it impossible to design windows when setting up the room, so most CT rooms use plasma air disinfection machines instead. Plasma air disinfection machine is a combination of plasma, filtration, electrostatic field and other disinfection measures, the core of its role is the plasma reactor, under the action of the strong electric field can destroy bacterial cell membranes, microorganisms and aerosols have a good killing effect, with high-efficiency sterilization, efficient degradation, low energy consumption, long service life, and other advantages, but also because of the easy operation, can achieve human-machine coexistence, not affected by personnel walking around, can Continuous dynamic disinfection, to make up for the shortcomings of the UV lamp, to achieve better disinfection requirements.

2) Selection of machine room characteristics and disinfection effects

According to the comparison of the 3 disinfection methods, although all 3 disinfection methods can achieve satisfactory disinfection effects, they cannot be relaxed during the epidemic and must be the best disinfection solution must be chosen. Pure plasma air disinfection machine has the weakest disinfection effect. The weakest effect was achieved by the plasma air disinfector alone, while the strongest effect was achieved by the combination of UV disinfection lamps; the UV lamps alone can also achieve satisfactory disinfection, but because they must be used when no one is around, the disinfection effect lasts forever. The disinfection effect is limited due to the fact that it must be performed when no one is around. Therefore, based on the maintenance of the CT room equipment and the sensitivity of 2019-nCoV to UV light, the recommended disinfection effect during the epidemic is to disinfect the CT room. Sensitivity of 2019-nCoV, the use of UVC lamps in combination with ISO ion air disinfection machine for air disinfection in dedicated CT rooms and for quality control management of the effective implementation of disinfection, and the development of specifications and The time and frequency of disinfection should be in accordance with the specifications and needs.

3) Quality control measures for the disinfection of dedicated CT rooms

(1) principles of disinfection: ① at any time and at regular intervals, with an average circulating air volume of ≥ 1 000 m³/h 24 h uninterrupted use of plasma air disinfection machine, at the end of the inspection, when no one is using UV disinfection lamp disinfection 60 min, 3 times a day; ② disinfection protection, UV disinfection when closing all doors and windows, prohibit personnel access, disinfection after the end of the static 10 min before entering; ③ multi-mode combination Disinfection, for the characteristics of 2019-nCoV, only air disinfection is not enough, but also need to combine with the disinfection of machinery and equipment, object surface and ground disinfection to achieve a perfect disinfection mode; ④ Personnel control, although a better disinfection method has been adopted, but still need to pay attention to the control of personnel entering the machine room, requiring staff to be secondary protection before entering the machine room, and patients with limited mobility should try to enter alone without Patients with limited mobility should not be accompanied by family members and enter alone to avoid cross-infection.

(2) Use and maintenance of equipment: select UV disinfection lamps that meet national standards, combine with “Technical Specifications for Disinfection in Medical Institutions” and actual needs, install suspended lamps, and supplement the lamp frame with polished aluminum reflectors; to ensure the effectiveness of disinfection, wipe clean the lamps with 75% alcohol every week. When applying the plasma air disinfection machine for uninterrupted dynamic disinfection, attention should be paid to circuit protection, and the machine can be temporarily shut down during UV disinfection; daily wipe clean the air outlet live leaf and machine surface with quaternary ammonium disinfection wipes.

(3) Monitoring and recording of disinfection: ① Implement accountability management, organize and prepare the “New Coronavirus Pneumonia Special CT Room Disinfection Registration Form”, record the UV lamp number, time of first use, start and stop time of each irradiation, and the cumulative length of irradiation. Time of first use, start and stop time of each irradiation, and cumulative duration of irradiation, etc.; ② Use of plasma air disinfection machine time, duration of use, and time of wiping clean equipment; ③ Regularly conduct (3) Regular air bacterial colony testing to ensure satisfactory disinfection results.

4 Conclusion

In order to fully respond to the 2019-nCoV epidemic and to ensure the dedicated CT machine room safety during use, the use of UV disinfection lamps combined with plasma air disinfection machine can achieve continuous circulation disinfection of the air in the CT room, which It can not only reduce the damage to the machine and equipment but also maximize the elimination of cross It is worthwhile to implement the disinfection method to ensure the safety of doctors and patients.

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