Virus World

There currently is substantial controversy about the role played by SARS-CoV-2 in aerosols in disease transmission, due in part to detections of viral RNA but failures to isolate viable virus from clinically generated aerosols. Methods - Air samples were collected in the room of two COVID-19 patients, one of whom had an active respiratory infection with a nasopharyngeal (NP) swab positive for SARS-CoV-2 by RT-qPCR. By using VIVAS air samplers that operate on a gentle water-vapor condensation principle, material was collected from room air and subjected to RT-qPCR and virus culture. The genomes of the SARS-CoV-2 collected from the air and of virus isolated in cell culture from air sampling and from a NP swab from a newly admitted patient in the room were sequenced.

Viable virus was isolated from air samples collected 2 to 4.8m away from the patients. The genome sequence of the SARS-CoV-2 strain isolated from the material collected by the air samplers was identical to that isolated from the NP swab from the patient with an active infection. Estimates of viable viral concentrations ranged from 6 to 74 TCID50 units/L of air. Patients with respiratory manifestations of COVID-19 produce aerosols in the absence of aerosol-generating procedures that contain viable SARS-CoV-2, and these aerosols may serve as a source of transmission of the virus.

As reported in air sampling tests performed by others and in our previous report, airborne SARS-CoV-2 was present in a location with COVID-19 patients. The distance from the air-samplers to the patients (≥ 2 m) suggests that the virus was present in aerosols. Unlike previous studies, we have demonstrated the virus in aerosols can be viable, and this suggests that there is an inhalation risk for acquiring COVID-19 within the vicinity of people who emit the virus through expirations including coughs, sneezes, and speaking.

Preprint available at medRXiv (August 4, 2020):

https://doi.org/10.1101/2020.08.03.20167395

A plea issued by 239 scientists from around the world to recognize and mitigate airborne transmission of COVID-19 addressed to international health authorities is to be published in the journal Clinical Infectious Diseases. The 239 signatories from 32 countries come from many different areas of science and engineering, including virology, aerosol physics, flow dynamics, exposure and epidemiology, medicine, and building engineering. Led by internationally recognized air quality and health expert QUT Professor Lidia Morawska, the appeal is to address the overwhelming research finding that an infected person exhales airborne virus droplets when breathing and talking that can travel further than the current 1.5m social distance requirement.

"Studies by the signatories and other scientists have demonstrated beyond any reasonable doubt that viruses are exhaled in microdroplets small enough to remain aloft in the air and pose a risk of exposure beyond 1 to 2m by an infected person," Professor Morawska, director of the International Air Quality and Health Laboratory, said. "At typical indoor air velocities, a 5-micron droplet will travel tens of meters, much greater than the scale of a typical room while settling from a height of 1.5m above the floor." Signatories to the appeal come from many disciplines including different areas of science and engineering, including virology, aerosol physics, flow dynamics, exposure and epidemiology, medicine, and building engineering. "Expertise in many science and engineering areas enables us to understand the characteristics and mechanisms behind the generation of respiratory microdroplets, how viruses survive in these microdroplets, and how airflow patterns carry microdroplets in buildings," Professor Morawska said.

The measures that need to be taken to mitigate airborne transmission include:

• Provide sufficient and effective ventilation (supply clean outdoor air, minimize recirculating air) particularly in public buildings, workplace environments, schools, hospitals, and aged care homes.
• Supplement general ventilation with airborne infection controls such as local exhaust, high efficiency air filtration, and germicidal ultraviolet lights.
• Avoid overcrowding, particularly in public transport and public buildings.

Original letter published in J. Clinical Infect. Diseases (July 6, 2020):

https://doi.org/10.1093/cid/ciaa939