Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks.

Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.

[Viral transmission in COVID-19: the role of the aerosol]. / Virustransmissie bij covid-19.

Since there is no adequate treatment for COVID-19, prevention of the transmission of SARS-CoV2 is the best way to cope with the pandemic. National guidelines for non-pharmaceutical interventions focus mainly on the interference with viral transmission via droplets and surface by hygiene measures, limitation of human contact, and social distancing. There is growing evidence that a third route of transmission by aerosols - exhaled tiny particles with viable infectious virus that remain airborne for hours - may be relevant. This route may even be the predominant way of viral transmission in the case of so-called superspreading events. It implies the need for adequate ventilation at indoor spaces without recirculation of virus containing aerosols. Here, the use of face-masks might be of added value too. These measures appear to be especially pivotal during episodes of colder weather, when people spend significantly more time indoors.