Airborne Transmission of Virus-laden Aerosols

COVID-19 is AIRBORNE! Prof. Chia C. Wang, Director of Aerosol Science Research Center, and Prof. Kimberly A. Prather, Director of the Aerosol Center at the University of California, San Diego, and the world-renowned infectious disease expert Dr. Robert T. Schooley jointly published a special article in Science, pointing out that SARS-CoV-2 can spread in the air in the form of very fine aerosol particles or droplets. In particular, asymptomatic patients do not know the infection, and do not wear any protective masks or protective measures, the transmission of aerosol may become the main route of infection.

COVID-19 continues to spread around the world. In terms of disease control and prevention strategies, there are still blind spots or incompleteness. At present, it is widely recognized by the public and recognized by the World Health Organization that the method of virus transmission is contact and droplet transmission. Based on this, the epidemic prevention guidelines for washing hands frequently and maintaining social distancing are set.

In the past, people believed that only when the patient coughed or sneezed, the droplets produced were at risk of infection. But in fact, when people talk, sing, cough, or even simply breathe, they will release many tiny droplets of aerosol below 1 micron in size. When the respiratory tract or lungs of COVID-19 patients contain SARS-CoV-2, these viruses can be released into the environment along with the breath glue. These virus-containing aerosol, if they are breathed into the respiratory tract or lungs by others while maintaining their infectivity, it may cause the virus to replicate in the new host and lead to the onset of infection.

The current safe social distance recommended by the WHO is estimated based on the droplets produced by patients coughing or sneezing. Looking back to its historical origin, the particle size of this type of droplet is mainly based on the measurement of W. F. Wells et al. in the 1930s. However, under the background of time and space 90 years ago, the measurement equipment and technology were not advanced enough, and the sensitivity was not enough to detect aerosol particles below 1 micron. As the times evolve, the technology for measuring micro and nanoscale particles has become more mature. The expiratory aerosol measured in experiments in the past 20 years have consistently pointed out that the size of the micro aerosol is less than 1 micro. Accounted for the most. When the fine aerosol containing the virus is released into the environment through the patient's breath, it can not only be suspended in the air for a longer period of time, but also more likely to spread to a greater distance than the safe social distance currently recommended by the WHO.

The article published in Science pointed out that for a droplet with a particle size of 100 micron, it takes only 4.6 seconds to fall from a height of 8 feet to the ground, but for an aerosol with a particle size of only 1 micron, it will drop from the same height to the ground. It took 12.4 hours on the ground. Recent studies have found that aerosols containing SARS-CoV-2 can survive in the air for at least 16 hours. These virus aerosols with smaller particle size, once inhaled into the human body, may also enter deeper into the human lungs and cause infection.

Many viral diseases, including severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (mers), H1N1 and other influenza viruses, have been confirmed by the literature that they can spread in the air in the form of aerosol. Novel coronavirus pneumonia novel coronavirus pneumonia has been reported since the end of 2019. So far, there are enough evidences, including experimental, field measurement and sampling analysis, epidemiological statistics, and aerodynamics simulation. All of these findings indicate that SARS-CoV-2 virus, which causes new crown pneumonia COVID-19, can indeed spread through air in the air. It is also mentioned in the special article published in science that the spread of aerosol will lead to the highest risk of infection when asymptomatic infected persons who do not know of the disease and others (possible hosts) around do not wear any protective masks or protective measures; Especially when it is in a regional closed or semi closed space with poor ventilation and high concentration of suspended virus aerosol. On the contrary, the risk of infection can be minimized when both the infected and the healthy uninfected wear masks.

Reference:

Kimberly A. Prather, Chia C. Wang, Robert T. Schooley, Reducing transmission of SARS-CoV-2, Science 368, 1422-1424 (2020). (link)