Personal breathing zone5/5/2023 Further, population-level community infection studies lend support to universal masking as a manner to reduce infectious disease transmission. Reduction in infectious transmission of SARS-CoV-2 by universal masking has been examined using computational modeling. Double masking, such as by wearing a 3-ply cotton cloth mask over a medical mask, can provide up to a 96% reduction in aerosol exposure compared to no masking, thus providing significant protection against the transmission of SARS-CoV-2. Modifications aimed to improve face mask fit can improve their performance. The combination of source masking and recipient masking for all individuals (called “universal masking”) can reduce exposure significantly more than when masks are just worn by a source or recipient. Donning a mask also may reduce the exposure of an uninfected wearer to aerosols from a potentially infectious source. Donning a mask can reduce the release of respiratory aerosols and droplets by 85% or more, depending on the mask and exhalatory event. Masking reduces the expulsion of respiratory aerosols and droplets from the point of generation. Centers for Disease Control and Prevention (CDC) recommends a combination of measures including universal mask wearing, increased room ventilation and filtration, and physical distancing. To reduce the risk of SARS-CoV-2 transmission in indoor spaces, the U.S. Since the critical dose threshold for SARS-CoV-2 infection is unknown, one goal of exposure mitigation is to reduce intensity, duration, or both as much as feasible. The risk of infection increases with the intensity and duration of exposure, as well as the concentration of active virus-laden respirable aerosols. During that time, potentially infectious aerosols suspended in the indoor environment may translate to exposure and possible transmission. These respiratory aerosols and droplets, the smallest of which may remain suspended in the air for several minutes to several hours, can disperse throughout the indoor environment. Aerosols have been defined as airborne particles 100 µm, which is the definition used in this investigation. SARS-CoV-2, the virus that causes COVID-19, can spread between humans by respiratory fluid aerosols and droplets released during exhalatory events, such as breathing, coughing, talking, singing, and sneezing. While universal masking remains a key component of a layered mitigation strategy of exposure reduction, increasing ventilation via system HVAC or portable HEPA air cleaners further reduces exposure. The results demonstrate that mitigation strategies, such as universal masking and increasing ventilation, reduce personal exposure to respiratory aerosols within a meeting room. Ventilation reduced exposure by approximately 5% per unit increase in air change per hour (ACH), irrespective of whether increases in ACH were by the HVAC system or portable HEPA air cleaners. While evaluating the effect of Source placement, Recipients had the highest exposure at 0.9 m in a face-to-face orientation. Universal masking of all breathing simulators with a 3-ply cotton mask reduced aerosol exposure by 50% or more compared to scenarios with simulators unmasked. Recipients, represented by three breathing simulators with manikin headforms, were placed in a meeting room and affixed with optical particle counters to measure 0.3–3 µm aerosol particles. To quantify exposure of uninfected individuals (Recipients), surrogate respiratory aerosol particles were generated by a breathing simulator with a headform (Source) that mimicked breath exhalations. Here, we examine the effect of mitigation strategies on reducing the risk of exposure to simulated respiratory aerosol particles within a classroom-style meeting room. Layered mitigation strategies, including but not limited to maintaining physical distancing, adequate ventilation, universal masking, avoiding overcrowding, and vaccination, have shown to be effective in reducing the spread of SARS-CoV-2 within the indoor environment. SARS-CoV-2 can spread by exposure to droplets and very fine aerosol particles from respiratory fluids that are released by infected persons. There is strong evidence associating the indoor environment with transmission of SARS-CoV-2, the virus that causes COVID-19.
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