2021-09-03

Research: Except for COVID-19, most respiratory viruses can actually be transmitted through aerosols

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Research: Except for COVID-19, most respiratory viruses can actually be transmitted through aerosols

In the last century and at the beginning of the pandemic, it was generally believed that respiratory viruses, including SARS-CoV-2, mainly passed through infected persons Droplets produced when coughing and sneezing or spread through contact with contaminated surfaces. However, the droplet transmission of SARS-CoV-2 cannot explain the large number of super-spreading events observed during the COVID-19 pandemic, nor can it explain the increased transmission that occurs indoors compared to outdoors.

Out of the desire to understand the factors that lead to the COVID-19 pandemic, researchers from Taiwan, the United States, and Israel have tried to determine as clearly as possible the spread of coronaviruses and other respiratory viruses. For example, the research team reviewed studies on a large number of super-transmission events observed during the COVID pandemic and found that these studies consistently show that airborne transmission is the most likely route of transmission, rather than surface contact or droplet transmission. A common factor in these super-spreading events is that people inhale air together in the same room.

Many super-spreading incidents are related to crowded locations, exposure times of one hour or more, poor ventilation, and incorrect wearing of masks. The researchers also reviewed the evidence gathered from many other types of research-air sampling, polymerase chain reaction (PCR) or cell culture-based research, epidemiological analysis, laboratory and clinical research, and modeling work- -And concluded that airborne transmission is a major or even dominant transmission route for most respiratory diseases, not just COVID-19.

“Transmission through inhalation of virus-containing aerosols has been ignored for a long time. The director of the Aerosol Science Research Center of Sun Yat-sen University in Taiwan, China, who led this review, said Wang Jiacheng, an aerosol physical chemist:” Now is the time to revise the traditional paradigm by implementing aerosol preventive measures to protect the public from this route of transmission. ”

Research: Except for COVID-19, most respiratory viruses can actually be transmitted through aerosols(1)

The research team pointed out that about The epidemic paradigm of the spread of respiratory diseases can be traced back a century ago. At the beginning of the 20th century, Charles Chapin, a well-known public health person, denied air transmission because he worried that mentioning air transmission would scare people into doing nothing and replace hygiene habits. Unfounded assumptions mistakenly equating close-range infection with droplet transmission, forming the current paradigm for controlling the spread of respiratory viruses. However, this assumption ignores the fact that aerosol transmission also occurs at short distances, because when people When you are closer to an infected person who emits aerosols, the concentration of exhaled aerosols is higher,” said Kim Prather, director of the National Science Foundation Center for the Chemical Impact of Aerosols on the Environment at the Scripps Institution of Oceanography, University of California, San Diego. Said that he is the co-leader of this review.

Respiratory aerosols are formed by exhalation activities, such as breathing, talking, singing, shouting, coughing and sneezing. Before COVID-19, The traditional size boundary between aerosols floating like smoke and dripping droplets is set to 5 µm. However, 100 µm is a more suitable size distinction. This updated size better represents The largest particle that is suspended in still air for more than 5 seconds (from a height of 1.5 meters), walks one meter away from an infected person, and is inhaled. “The physical size mainly determines how long they can be suspended in the air. How far to reach, whether it can be inhaled, and if it is inhaled, how deep into the respiratory tract. “Most of the aerosols produced by respiratory activity are smaller than 5 µm, which allows them to penetrate deep into the bronchi and alveolar areas and deposit there. Studies have found that the virus is contained in aerosols smaller than 5 µm in higher levels,” Technion of Israel Lung physiologist Josué Sznitman said.

Another unique behavior of aerosols that should be seriously considered is their ability to be affected by airflow and ventilation. Ensuring adequate ventilation rates, filtering and avoiding recirculation can help reduce the spread of infectious virus-bearing aerosols in the air. Jose-Luis Jimenez, an atmospheric aerosol chemist at the University of Colorado Boulder, added: “Monitoring carbon dioxide with portable meters helps to verify that ventilation is adequate, as are the implementation of portable HEPA (High Efficiency Particulate Air) purifiers and UV disinfection systems for upper rooms. Helps reduce the concentration of virus-carrying aerosols. “On the other hand, the plexiglass barriers that are usually used to block the droplets from indoor coughs and sneezes may “block proper ventilation and cause higher exposure to some people.” Linsey Marr of Virginia Tech, who has been studying the spread of pathogens in the air for many years, said. “Except for short-term, face-to-face transactions, masks are not recommended, but even so, masks are better because they help to remove aerosols, and the barrier just transfers them.”

As Delta changes The surge in infections caused by humans, and the continuous occurrence of “COVID-19 breakthrough cases” (infections that have occurred in people who have been fully vaccinated), many governments and national disease control agencies have restored the regulations to wear masks in public places. The commentary reported that wearing a mask is an effective and economical way to block virus-carrying aerosols. However, “we need to consider multiple transmission barriers, such as vaccination and ventilation.” Seema S. Lakdawala, a virologist at the University of Pittsburgh, added: “A single strategy is unlikely to be strong enough to eliminate the emerging SARS-CoV-2. The spread of variants.

As evidence of SARS-CoV-2 spread through the air has increased over time and has become particularly strong, agencies have taken note. In April and May 2021, the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) recognized that inhaling virus-carrying aerosols is a major way to spread COVID-19 over short and long distances. This means that in order to reduce the spread and end this pandemic, policymakers should consider implementing aerosol preventive measures, including universal wearing of masks and paying attention to the fit of the masks, increasing the ventilation rate of indoor spaces, and avoiding the recurrence of polluted indoor air. Circulation, install air filter device, such as HEPA purifier, can effectively remove particles in the air, and use ultraviolet disinfection lamp. Zeynep Tufekci, a sociologist at Columbia University who studies the social challenges of the COVID-19 pandemic, pointed out: “What has traditionally been called droplet prevention measures has not been completely replaced, but has been carried out in a more effective manner based on the actual transmission mechanism. Modifications, expansions and deployments.” She added that having the right mental model for the spread of this disease and other respiratory diseases will also enable ordinary people to make better decisions in daily situations and enable administrative staff and officials to After a pandemic, better guidelines and working and social environments can still be created.

This pandemic vividly illustrates the importance of the long-underestimated route of air transmission and the need to maintain people’s right to breathe clean and pathogen-free air. “What we have learned from this pandemic also illuminates the way we can make appropriate changes to enter the post-pandemic era,” the researchers said. As stated at the end of the review, these aerosol preventive measures can not only prevent the airborne transmission of respiratory diseases, but also improve indoor air quality and bring health benefits far beyond the COVID-19 pandemic.