Long-range and short-range risk of airborne transmission of SARS-CoV-2

The pandemic of COVID-19 caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) contributes to significant morbidity, mortality, and financial loss. To date, the virus has infected more than 159 million people and killed more than 3.3 million people worldwide. The need to mitigate this pandemic has led the scientific community to reassess its infectivity, mechanism, and risk of infection under certain conditions.

Recent research shows Florian Poydenot et al. We conducted a quantitative assessment of the risk of infection indoors and outdoors. And how to reduce the contribution of public space to the propagation of SARS-CoV-2.The study is published in medRxiv*, Health science preprint server.

“Quantitative analysis of the risk of viral infection in public places can identify the key mechanisms by which preventative public health policies can act to mitigate risk and assess the resulting risk mitigation.”

Researchers have shown that long-range aerosol propagation is controlled by fresh air flow and mask filtration quality and is quantitatively associated with CO2 concentration, regardless of room volume or number of people. .. Importantly, they found that it was quantitatively related to CO2 concentration, regardless of room volume or number of people.

Researchers have ly investigated short-range aerial transmission using dedicated distributed experiments conducted at two shopping malls. They found that the exhaled aerosol was dispersed by a conical turbulent draft, leading to a concentration that was inversely proportional to the square of the distance and the flow velocity.

They elaborated on the various technologies available to reduce the risk of viral infections in public places. In this study, researchers showed that an average infection level, called a viral quantum, could be determined from epidemiological data (in a manner consistent with biological data).

In this study, researchers defined and modeled transmission risk, focusing on indoor and outdoor long-range aerial transmission risk (measured using carbon dioxide concentration) and short-range aerial transmission risk. .. They investigated the quantum generation rate and dose-response function.

They also investigated the efficiency of respiratory masks based on droplet size distribution, droplet evaporation (controlled by ambient relative humidity RH), and concentration issues.

SARS-CoV-2 can easily spread during exhaled human activity (breathing, talking, singing, laughing, etc.) and can cause asymptomatic and presymptomatic infections (as aerosols). It has been established. It has also been observed that indoor infections are 19 times more common than outdoors.

Measuring the risk of virus infection in public places (schools, offices, university auditoriums, museums, theaters, shopping centers, etc.) and outdoors is a problem. Researchers in this study have sought to characterize major transmission routes in social activities and identify efficient ways to reduce the risk of epidemic contamination in public spaces.

In this comprehensive study, researchers define the risk of infection in public places to the number of people present, the average time they are present, the amount of aerosol stored, and the level of ventilation. Document the dependencies of.

They determined a risk assessment for long-range aerial transmission and associated it quantitatively with CO2 levels.

Interestingly, this study showed that localized short-range aerial transmission after people infected with SARS-CoV-2 follows the same physics indoors and outdoors.

Experimental measurements of turbulent dispersion of passive tracers (CO2) performed in shopping centers have shown that turbulent diffusion is due to small permanent airflows leading to rapid spatial decay of tracer concentrations. They report that the additional risk of waking up from others is quantitatively determined as a function of leeward distance.

In conclusion, researchers provide a practical definition of risk r (Defined as the average secondary infection per person who was first infected) Related to public spaces. This is related to the integrated quantum emission, mask filtration factor (λ), and CO2 concentration that quantifies the dilution factor between exhaled air and inspiratory air.

Based on this risk assessment, researchers have defined quantitative criteria (occupancy, CO2 levels, ventilation, masks) to be implemented in public spaces to reach acceptable residual risk.

The goal of efforts to mitigate COVID-19 is to reduce the pandemic to a level where the overall virus regeneration rate is less than one. This study prevents major routes of viral infection through enhanced ventilation, air purification, and mechanical dispersion using fans, and may be covered with properly fitted high quality facial masks (surgical masks). There is another fabric mask, or by a non-medical FFP2 mask).

Combining these measures will significantly reduce the risk of SARS-CoV-2 transmission in the air.

*Important Notices

medRxiv Publish preliminary scientific reports that should not be considered definitive as they are not peer-reviewed, guide clinical practice / health-related behaviors, and should not be treated as established information.