COVID-19 Viral Loads, Environment, Ventilation, Masks, Exposure Time, And Severity : A Pragmatic Guide Of Estimates

Epperly, D. E.; Caney, D. N.

It is desirable to better characterize and understand how ventilation improvements in office spaces could offer significant protection against transmission of COVID-19. It is also desirable to understand how ventilation in office spaces compares to outdoor settings. An attempt to find this information from online searches that included medical journals, private industry, and US government provided materials failed to find specific quantitative estimates and recommendations, which motivated this study. This study uses measured amounts of SARS-CoV-2 in the air of a hospital room with COVID-19 patients from a published and peer-reviewed study and known Influenza A challenge doses from a published and peer-reviewed study and known ASHRAE Office Ventilation standards and an Outdoor Air Exchange model to estimate the time necessary to cause various exposure levels and resulting infection potential in various indoor and outdoor settings of both Influenza A and COVID-19. While these estimations have unknown error margins and cannot be considered authoritative, they may have utility in comparing various environments and relative risk factors. The estimates in this study also present an initial framework and specific quantitative examples for better understanding of the effects of ventilation on aerosolized transmission, and the immunology related to challenge doses, and the potential for low-level viral load exposure to result in some level of immunity without symptoms of illness (asymptomatic infection). Specific quantitative examples of exposure viral load versus symptoms and immune response may Increase public understanding and consciousness of concepts such as viral load, exposure time, challenge dose levels, shedding quantities, immune seroconversion, and re-challenge and could achieve new levels of personal hygiene that complement centuries-old adages such as wash your hands.