Recently, aerosol transmission has once again attracted attention, and Taierzhuang and Ningbo officials have issued notices reminding them of the risk of aerosol transmission of the new crown virus.
On April 10, the Ningbo Center for Disease Control and Prevention issued a notice that a case in Ningbo was infected after entering an underground parking lot with a car window and without a mask, and two other cases stayed in the parking lot and did not wear a mask during the same time period, which was judged to be an infection caused by aerosol transmission.
On April 12, the office of the Taierzhuang District Party Committee's Leading Group (Headquarters) for Coordinating Epidemic Prevention and Control and Economic Operation issued an urgent reminder that when a resident of Taierzhuang went to dig wild vegetables somewhere outdoors, he was infected after staying with an asymptomatic infected person, and both of them did not wear masks.
The Ningbo Municipal Center for Disease Control and Prevention announced that it will strengthen the prevention and control of crowded areas such as public services and construction sites and public transportation. The Taierzhuang District Party Committee's Leading Group for Coordinating Epidemic Prevention and Control and Economic Operation (Headquarters) issued an urgent reminder calling on residents to wear masks when going out.
On April 13, Qian Hua, a professor at the School of Energy and Environment of Southeast University and vice chairman of the Indoor Environment and Health Branch of the Chinese Environmental Society, pointed out in an interview with Red Star News that outdoor air is diluted and long-distance aerosol transmission is very rare, in the case of Taierzhuang, both did not wear masks, if close, do not rule out the possibility of aerosol transmission, but further analysis is needed.
Qian Hua said that due to the greatly enhanced transmission capacity of Aomi Kerong, it is more recommended to wear N95 masks in areas where the epidemic is running at a high level. At the same time, pay attention to hand disinfection and window ventilation.
Did the aerosol spread caused by Omicron become worse?
Experts: Outdoor long-distance transmission is rare, and N95 masks and window ventilation are more recommended under TheOmilon
Did the aerosol spread caused by Omicron become worse?
Li Yuguo, deputy dean of the School of Engineering at the University of Hong Kong and an expert in indoor air and fluid mechanics, said in an interview with Red Star News that there was no qualitative change in the physical transmission route of Omi Kerong, at least no transmission between buildings of more than 10 meters was observed. Its increased ability to spread may be more due to changes in its biological properties.
Li Yuguo pointed out that the risk of outdoor transmission of the new crown virus is very low, and this risk is also related to whether there is sun and outdoor air stratification. Theoretically, the risk of close outdoor transmission in Aumechon increases.
Qian Hua, a professor at the School of Energy and Environment of Southeast University and vice chairman of the Indoor Environment and Health Branch of the Chinese Environmental Society, also pointed out that the outdoor air is diluted and long-distance aerosol transmission is very rare, in the case of Taierzhuang, both did not wear masks, if close, do not rule out the possibility of aerosol transmission, but further analysis is needed.
In this round of the epidemic dominated by Omikerong, there have been "super-spreaders" in some parts of the country, and the number of viruses carried is high and the risk of transmission is large. In January 2022, a study published in swiss medical weekly on the risk of aerosol transmission in Omikejong showed that "super-spreaders" were more likely to appear among Omiljung's infected people than previous strains, with 1 case of "super-spreaders" in every 20 infected people or every 10 infected people. In addition, due to their greater infectivity, medical masks have a weaker blocking effect on the spread of the Omiljun virus, especially aerosol transmission. In many cases where there is a risk of aerosol transmission, the spread of wild and Delta strains can be prevented by wearing a medical mask, while the Olmiqueron strain is difficult to prevent.
In this regard, Qian Hua said that due to the greatly enhanced transmission ability of Omicron, it is more recommended to wear N95 masks in areas where the epidemic is running at a high level. At the same time, pay attention to hand disinfection and window ventilation, but the windows facing the relatively closed outdoor spaces (such as patios, semi-patios) are not opened.
Li Yuguo said that the spread rate of Omicron has increased by 4-5 times, and the interior is more dangerous than before. He previously recommended 8-10 liters of ventilation per person per second in the room, and now this number is multiplied accordingly, perhaps exceeding the mechanical ventilation capacity, which shows the importance of window ventilation.
The Beijing CDC paper shows that vertical transmission upstairs and downstairs occurs in hotels or upstairs
Experts say the risk of vertical transmission of Omi kerong may be elevated
On 11 April, the Chinese Journal of Epidemiology published a study by the Beijing Center for Disease Control and Prevention that in November 2021, a case in Changping District, Beijing, may have been infected by a confirmed case downstairs through aerosol transmission in a bathroom ventilation duct while isolating in an isolation hotel. The study ruled out other sources of infection through epidemiological investigations and was positive for nucleic acids in environmental specimens deep inside the vent ducts and had a 100% similarity to viral nucleotides in cases in both rooms. The study found that the isolation hotel was old, with ventilation ducts connecting up and down and ventilation duct openings open.
The vertical spread of this isolated hotel in Beijing is reminiscent of the vertical spread of the floors of Amoy Garden in Hong Kong during the SARS period in 2003. Li Yuguo was the researcher who confirmed the vertical spread of aerosols through field measurements at that time.
Li Yuguo said that in vertical buildings, when wastewater from toilets and washbasins is discharged, aerosols are produced in the sewage pipes, that is, atomizations containing feces, urine and secretions from the mouth and nose. The chimney effect explains the long-distance transport of pipe aerosols. The chimney effect refers to the phenomenon that indoor air rises or falls along a space with a vertical slope, causing air to convect.
▲ Sewage discharge produces aerosols, and the chimney effect causes the air flow to transport aerosols vertically upwards According to the paper
Li Yuguo told Red Star News that as of January 2022, before the outbreak of the epidemic in Aumequeron, he had observed 15 clusters of cases related to pipeline aerosols in high-rise buildings in Hong Kong, Guangzhou and other places. His team measured 6 of them with gas tracers.
An article co-authored by Academicians Li Yuguo, Qian Hua and Zhong Nanshan, as well as researchers from the Guangdong Center for Disease Control and Prevention, examines the cluster outbreak that occurred in a high-rise building in Guangzhou in 2020 and also supports the theory of fecal-aerosol transmission.
Li Yuguo said that before TheOmilon, the probability of vertical transmission was very low, about 1%, but in this Hong Kong epidemic, many buildings continued to spread after the closure, indicating that the risk of vertical transmission increased.
In addition, the new crown virus in the building may also be transmitted through the ventilation of doors and windows to produce a horizontal aerosol transmission. An unpublished study of the epidemic in Luquan Lou, a public housing complex in Hong Kong, by Li Yuguo's team, shows that when the doors and windows of the apartments directly downwind of the confirmed cases are opened by 20%, the concentration of viral aerosols in their houses will increase by 2 times. The building's floor plan is similar to that of the Isolated Hotel, providing a possible explanation for the spread in the Isolated Hotel. The article recommends taking positive pressure and adequate ventilation.
According to the study, it can be seen that aerosol transmission in buildings, especially in buildings with high degree of tightness, is easy to occur through various channels.
How to prevent the spread of sewage pipes?
Expert: Ensure that the toilet floor leaks water seal
Li Yuguo is very worried about the spread of aerosols caused by sewage pipes. When spitting in the wash basin and brushing teeth and gargling, saliva containing the new crown virus will follow the flow of water into the riser tube, which is difficult to prevent.
"According to the hygiene habits of East Asians, 25% of people spit on the wash basins of public toilets. Then, try not to throw up, it is best to spit into a tissue, wrap it up in a plastic bag, and pay attention to oral cleaning. Li Yuguo said.
Qian Hua said that in many commercial buildings, pipeline wells, exhaust pipes, and sewage pipelines are independent, but they are vertically connected and need to be maintained and inspected. The designed exhaust duct draws the air outward and has a check valve to prevent backflow.
In order to prevent infection between buildings in residential buildings, Qian Hua pointed out that the bathroom air outlets of general households are independent, but the sewage pipes are connected, so there is a risk of vertical transmission. He suggested that the bathroom floor should be guaranteed to leak water seals.
"The daily punt that will be sewn into the water, especially the less commonly used floor drain, is injected with water, and the S elbow can prevent the air flow from spreading. The water on the infrequently used floor drain can be blocked (such as using a plastic bag to fill the water tightly, placing it on the floor drain to seal, and opening it when it is used), reducing the evaporation of the water seal to avoid the water seal from drying out and failing. If the toilet smells not from your own home, check the passage with special care, it is likely that one of the sewers does not have an S elbow, or the S elbow water has dried. ”
Source: Red Star News client