Aerosol transmission of COVID-19 and infection risk in indoor environments

Abstract

The role of aerosolized SARS-CoV-2 viruses in airborne transmission of COVID-19 is debated. The transmitting aerosol particles are generated through the breathing and vocalization by infectious subjects. Some authors state that this represents the dominant route of spreading, while others dismiss the option. Public health organizations generally categorize it as a secondary transmission pathway. Here we present a simple, easy-to-use spreadsheet algorithm to estimate the infection risk for different indoor environments, constrained by published data on human aerosol emissions, SARS-CoV-2 viral loads, infective dose and other parameters. We evaluate typical indoor settings such as an office, a classroom, a choir practice room and reception/party environments. These are examples, and the reader is invited to use the algorithm for alternative situations and assumptions. Our results suggest that aerosols from highly infective subjects can effectively transmit COVID-19 in indoor environments. This "highly infective" category represents about one fifth of the patients tested positive for SARS-CoV-2. We find that "super infective" subjects, representing the top few percent of positive-tested ones, plus an unknown fraction of less, but still highly infective, high aerosol-emitting subjects, may cause COVID-19 clusters (>10 infections), e.g. in classrooms, during choir singing and at receptions. The highly infective ones also risk causing such events at parties, for example. In general, active room ventilation and the ubiquitous wearing of face masks (i.e. by all subjects) may reduce the individual infection risk by a factor of five to ten, similar to high-volume HEPA air filtering. The most effective mitigation measure studied is the use of high-quality masks, which can drastically reduce the indoor infection risk through aerosols.

The Impact of Large Mobile Air Purifiers on Aerosol Concentration in Classrooms and the Reduction of Airborne Transmission of SARS-CoV-2

“…Furthermore, the particulate matter PM 10 and the CO 2 concentration were measured during school operation. Based on a computational model by [ 49 ] and the measurements of the study, it was determined that the potential amount of virus-laden particles inhaled by people in the room is reduced by a factor of 6 through the use of APs. Here, a highly infectious person was assumed to spend two hours with other people in a room where APs with a total air-circulation rate of 5.7 h −1 were in operation.…”

Food Safety and Employee Health Implications of COVID-19: A Review

“…There has been significant discussion around role of aerosolized droplets, those with a diameter of <5 µm, and their ability to spread infectious virions across larger distances and times, and the need of ventilation systems to mitigate this potential route of transmission (5,98). A number of modeling studies have looked at various factors like droplet size, viral shedding rate, air flow, room dimensions, and types of ventilation systems to predict and highlight the potential risk of aerosolized transmission and infection in indoor environments (49,90,123,125). In the real world, unambiguous evidence of aerosolized transmission is difficult, but a number of outbreak studies have suggested that poor ventilation and air flow were contributing factors in SARS-CoV-2 transmission in a wide range of environments including food processing facilities (69), restaurants (96), apartment buildings (77), nursing homes (51) and hospitals (43), with environments like the latter, where infected individuals shedding high amounts of virus undergo procedures that would promote aerosolization, being a greater risk for such transmission.…”

The impact of large mobile air purifiers on aerosol concentration in classrooms and the reduction of airborne transmission of SARS-CoV-2

“…A key parameter for evaluating certain measures or influences is the risk of infection. However, determining the risk of infection from airborne aerosols is itself subject to some uncertainty (Lelieveld et al, 2020). For this reason, we do not focus on the risk of infection for our subsequent assessments, but rather on the inhaled particle dose, which represents the number of virus-laden particles ingested by a person.…”

“…Furthermore, the particulate matter PM10 and the CO2 concentration were measured during school operation. Based on a computational model by (Lelieveld et al, 2020) and the measurements of the study, it was determined that the potential amount of virus-laden particles inhaled by people in the room is reduced by a factor of 6 through the use of APs. Here, a highly infectious person was assumed to spend two hours with other people in a room where APs with a total air-circulation rate of 5.7 h -1 were in operation.…”