Findings from studies conducted to understand the aerosol transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the viral pathogen cause of COVID-19, provide a basis of recommendations for preventing infection spread.

In a letter to the editor of the New England Journal of Medicine, Matthew Meselson PhD, reviewed the role of liquid droplets and aerosol particles in the transmission of SARS-CoV-2. He concluded that the information suggests the advisability that persons wear a suitable mask to protect against infection when they may be nearby anyone who may be infected.  In addition, it supports the need for adequate ventilation to protect non-infected people who are in enclosed areas where infected people are known to be present or may have been present recently.

Dr Meselson is a molecular biologist and Thomas Dudley Cabot Professor of the Natural Sciences, Harvard University, Cambridge, MA, USA. His letter was published online April 15, 2020.

Dr Meselson cited a study that used laser light scattering to visualise oral liquid droplets that are exhaled while speaking. He noted these are relatively large particles that settle relatively quickly because of gravity. Because of their airborne behaviour, the droplets can transmit the virus either to someone nearby who inhales the particles before they settle or if a person touches a surface on which the particles settle and then touches their nasal or oral mucous membranes.

In contrast to the droplets, virions can also be exhaled within smaller aerosol particles during normal talking or breathing. The aerosol particles do not settle quickly because of gravity and instead may be carried considerable distances in the air. These smaller aerosol particles appear to be produced in greater quantities by so-called “super spreaders” and may pose an even greater infectious threat than the droplets considering differences in their sites of deposition within the respiratory tract, according to Dr Meselson.

He explained that while the particles deposit in the upper respiratory tract and tend to be expelled or swallowed, once the smaller aerosol particles are inhaled, they are able to pass down to the lung alveoli. Notably, results of another recent study showed that SARS-CoV-2 virions in experimentally created aerosols maintained infectivity in tissue cultures for at least three hours. Collectively, the information suggests that the aerosol particles expelled by persons infected with SARS-CoV-2 may pose a threat for disease transmission even to people who are a considerable distance away and to those who are in an enclosed space, particularly if there is poor ventilation.