The new coronavirus can be spread through aerosols, but it usually occurs in confined spaces
The so-called "handshake building" refers to a building where the distance between the building is close enough to open the window to shake hands
Researchers have suggested that under certain conditions, there is a risk of aerosol transmission of the new coronavirus in the centralized quarantine and home quarantine in the "handshake building"
The above content is from "Field Simulation of Aerosol Transmission of SARS-CoV-2 in a Special Building Layout — Guangdong Province, China, 2021).
Previously, many studies have confirmed that the new coronavirus can be transmitted through aerosols, but transmission usually occurs in confined spaces
Index case refers to the earliest case discovered and reported in an epidemic
The index case and the close-knit case before diagnosis lived in two different buildings of the hospital at the same time
The results show that there are obvious aerosol transmission paths from the close contact person’s residence and the index case’s residence, and its transmission is mainly affected by the airflow layout such as the opening and closing of the air conditioner and the opening and closing of doors and windows
The researchers selected 6 locations in the hospital for field experiments
Location 1 and location 2 are located in the fever clinic building
Location 3 is the outpatient department of Chinese medicine, where the index case is treated, and the window is open at the time; location 4 is a patient waiting area with an open window; locations 5 and 6 are the doctor's office and the consultation room, respectively, with the windows closed
Considering the influence of the airflow layout, the researchers set up 6 simulation scenarios, namely the opening and closing of the air conditioner in ward 1 (A), the opening and closing of the door in ward 1 (B), and the opening and closing of the windows in corridor 2 (C)
The researchers chose a pseudovirus model with a spike structure similar to the new coronavirus, a polystyrene fluorescent microsphere with similar aerodynamic properties
At the same time, the study monitors the concentration of different particle sizes and air conditions at 6 locations every 10 minutes
In the external layout of the building, the second floor is the fever clinic floor, and the fifth floor is the regular outpatient floor
In the internal room layout of the building, locations 1-6 are test locations
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The triangle (ac) is the factor that affects the air distribution: (a) air conditioner, (b) door; (c) window
.
The red dot is where the atomizer is located
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The fan symbol indicates that the air conditioner is turned on
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The green particles are fluorescent microspheres, simulating the virus aerosol and transmission and diffusion path exhaled by the index case
.
The simulation experiment obtained a total of 7411 field data and 304 samples, including 210 cotton swab samples for wiping the surface of objects, 54 aerosol liquid samples, and 40 aerosol filter membrane samples
.
In Ward 1, atomized fluorescent microspheres were used to simulate the breathing of the infected person, and the spread of the corridor at Site 2 and the room opposite to Site 3 was observed through the changes in the concentration of aerosol particles.
The results are shown in Figure 2
.
In the ward, the particle concentration of 1,0.
3µm increased significantly and remained stable after rising to the highest level
.
The particle concentration of 0.
5µm, 1µm, 2.
5µm, 5µm and 10µm also remained stable .
After the fluorescent microspheres are atomized, the particle concentration in the corridor starts to rise immediately and remains unchanged after reaching the highest value
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Compared with the change in ward 1, the peak time of particle concentration in location 3, the opposite room, is relatively delayed
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20-40 minutes after the fluorescent microspheres are atomized, the particle concentration in the opposite room at location 3 begins to rise
.
During the monitoring period, only the peak concentration was detected, and the plateau period of high concentration was not detected
.
In some cases, there was no significant change in the particle concentration at location 3, the opposite room
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At the same time, fluorescent microspheres were detected in the aerosol filter membrane samples, aerosol liquid samples and swab samples collected at the above three locations (Figure 3)
.
The results show that from ward 1 to the corridor to the opposite room, the entire aerosol transmission chain has been proven to exist
.
The researchers evaluated the effects of (A) air conditioners, (B) doors and (C) windows on aerosol propagation through 6 different scenarios
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The results showed that when the air conditioner, doors and windows were all closed, after atomizing the fluorescent microspheres in Ward 1, no fluorescent microspheres were found in the air filter membrane samples and liquid samples in Room 3
.
Studies have shown that when the airflow is poor, the fluorescent microspheres are not easily diffused into Room 3
.
When the air conditioner, doors and windows were turned on, the fluorescent microspheres quickly spread to Room 3
.
As long as the air conditioner is turned on, the airflow circulates in the ward, even if the doors and windows are closed, the particle concentration in the corridor and room 3 slowly rises
.
Once a door is opened, the particulate matter in the corridor can rise to the highest concentration within 5 minutes, but the change in the particulate matter concentration in Room 3 has little effect
.
Once the window is opened, even if the door is closed, the particle concentration in Room 3 will rise rapidly and significantly
.
In addition, with the air conditioner turned on, the influence of doors, windows, and movement of people on the spread of aerosols to Office 5 and Room 6 near Room 3 was studied
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During the experiment, people leave room 3 and enter the waiting area and room 6 every 10 minutes
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The results showed that when the windows were closed in the waiting area, office 5 and room 6, no fluorescent microspheres were detected in the aerosol filter membrane samples and liquid samples
.
Once the windows were opened, fluorescent microspheres could be detected in the samples in the waiting area and room 6, but no fluorescent microspheres were detected in office 5 because no one entered or exited office 5
.
It can be found that the risk of aerosol transmission in the "handshake building" is low when the windows on the opposite side of the building are closed
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Focus on the new crown pneumonia epidemic
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