ASRC: Poor ventilation may contribute to virus spread
In April, WHO confirmed that aerosol transmission (or airborne transmission) is the main route of transmission of SARS-CoV-2. Taiwan has recently experienced the most serious local epidemic outbreak so far. Director of Aerosol Science Research Center at NSYSU, Associate Professor Chia C. Wang and Director of the Center for Global Health at Oregon State University Chunhuei Chi pointed out that inadequate ventilation systems can facilitate the transmission of the virus and said that improving the filtration and disinfection of indoor air can reduce the risk of transmission by virus-laden aerosols floating in the air indoors. Improving indoor ventilation, and preventing circulation of dirty air indoors, installing a filter that can filter out airborne particles, such as a HEPA air purifier or a UVC air sterilizer that can effectively control the activity of the virus, are good ways to lower the risk of virus transmission indoors.
Director Wang emphasized that aerosols are fine liquid droplets or solid particulate matter suspended in the air. People release aerosols of diameter below 5 µm when they speak, sing, cough, and simply breathe. It is especially concerning when people infected with COVID-19 release virus-laden aerosols into the environment via these expiratory activities. In its physical state, aerosols can be seen as a micro version of the usual droplets. As for their difference in size, aerosols are not affected by gravity as much as liquid droplets, which fall to the ground within seconds. Aerosols with a small diameter can stay suspended in the air for hours or longer by the air’s drag force; and with airflow or the wind blowing, aerosols can be transported transmit further than the standard social distance. Once inhaled by a possible host, small virus-laden particles may cross the nasopharynx, the upper respiratory tract, and reach deeper into the bronchi of the lungs; and even the pulmonary alveoli and not be detected by current nasopharyngeal screening. Therefore, it is impossible to completely stop the spread of the virus only by taking precautions against the transmission by droplets or contact transmission. Director Wang mentioned, “This explains why many confirmed cases, both in Taiwan and overseas, have been infected despite having kept social distance and worn masks.”
“Another important difference between aerosols and droplets is that aerosols can be affected by the ventilation system to a much greater degree than droplets.” Director Chia C. Wang said that aerosols floating in the air can spread beyond the regulated social distance with factors such as various speeds of the exhalation airflow due to different activities (such as regular breathing, singing), the airflow or wind direction in the surrounding area, the indoor ventilation system, and even with the design of central air conditioning in the building. She further said that although ultraviolet light (UVC) effectively kills viruses, it needs to be installed in appropriate locations, such as on top of the room, inside the air purifier, or inside the air conditioning system to avoid direct radiation on people’s skin or eyes. Moreover, new buildings in the future shall have enhanced ventilation systems to reduce the risk of respiratory infections caused by poor ventilation and the risk of aerosol transmission of infectious diseases.
We can sum up the COVID-19 situation with a quote from “The Little Prince”: “What is essential is invisible to the eye.” The COVID-19 pandemic has proved that connections between people have become more far-reaching and close than ever before. Director Chunhuei Chi of the Center for Global Health at Oregon State University mentioned in the article “A paradigm shift to combat indoor respiratory infection,” published by Policy Forum of Science, a world-renowned journal, although public health systems around the world established comprehensive norms for the prevention and control of diseases caused by food and water in the past, airborne diseases have been relatively neglected. In the wake of the global COVID-19 pandemic, the importance of airborne transmission of pathogens in the form of aerosols has been more strongly noted and confirmed than ever before. Therefore, current insufficient protective regulations and systems should be improved for a better future indoor air quality and to prevent respiratory infections caused by poor indoor ventilation.
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