Almeida Susana Marta, Sousa João
Centro de Ciências e Tecnologias Nucleares. Instituto Superior Técnico. Loures. Portugal.
Green Building Energy Efficiency Laboratory Technology. Porto. Portugal.
Acta Med Port. 2021 Dec 2;34(12):815-825. doi: 10.20344/amp.15982. Epub 2021 Nov 8.
This study estimates the risk of aerosol infection by SARS-CoV-2 in indoor environments where high density of occupation results in an increased probability of infection, such as schools, offices, supermarkets, restaurants and gyms.
In each type of building use, several conditions were simulated, such as the use and effectiveness of masks, ventilation, use of equipment that allows air asepsis using HEPA filters, the density of occupancy and the length of stay in the spaces, using a model based on the dispersion of aerosol particles in indoor spaces and on the accumulation and inhalation of these particles over time.
The results showed that the replacement of social masks by masks with FFP2 classification decreased the risk of infection by 90% in schools. In schools with natural ventilation, the complete opening of windows reduced the risk of infection by 64% in comparison with the scenario with closed windows. In spaces where mechanical ventilation is normally used, the probability of infection decreased significantly when the regulatory fresh air flow rates were doubled (reduction of 32% in offices, 42% in restaurants, 24% in supermarkets and 46% in gyms). The filtration of air with HEPA filters allowed the reduction of the probability of infection by 72% in schools, offices, and restaurants and 61% in gyms. The length of stay in the spaces was also a relevant factor in the variation of the probability of infection, especially in schools where it was found that shorter classes with a higher number of intervals reduced the risk of infection.
The results show the importance of adequate ventilation in indoor environments, especially in places where the density of occupation and the staying times are longer, making the introduction of outside air inside the spaces essential, either through natural or mechanical means. It is expected that the infection risk estimates presented are undervalued because the model only considers transmission by particles smaller than 10 μm and does not include the short-range transmission by assuming social distancing. Vaccination was not considered in the model since it was not yet available when the study was carried out.
The present study contributes to the identification of measures that decrease the risk of viral transmission, and consequently provide greater security in indoor spaces.
本研究评估了在学校、办公室、超市、餐厅和健身房等高人员密度室内环境中，严重急性呼吸综合征冠状病毒2（SARS-CoV-2）通过气溶胶感染的风险，此类环境中感染概率会增加。
针对每种建筑用途，模拟了多种条件，如口罩的使用及效果、通风情况、使用带有高效空气过滤器（HEPA）实现空气无菌的设备、人员密度以及在空间内的停留时长，采用了基于室内空间气溶胶颗粒扩散以及这些颗粒随时间的累积和吸入情况的模型。
结果表明，在学校中，用FFP2级口罩取代普通口罩可将感染风险降低90%。在自然通风的学校，与窗户关闭的情况相比，窗户完全打开可将感染风险降低64%。在通常使用机械通风的空间中，当将规定的新鲜空气流量加倍时，感染概率显著降低（办公室降低32%，餐厅降低42%，超市降低24%，健身房降低46%）。使用HEPA过滤器过滤空气可使学校、办公室和餐厅的感染概率降低72%，健身房降低61%。在空间内的停留时长也是感染概率变化的一个相关因素，尤其是在学校，发现课时较短且课间休息次数较多可降低感染风险。
结果表明室内环境中充分通风的重要性，尤其是在人员密度高且停留时间长的场所，通过自然或机械方式引入室外空气至关重要。预计所呈现的感染风险估计值被低估了，因为该模型仅考虑小于10微米颗粒的传播，且未通过假设保持社交距离来纳入短程传播。由于开展研究时疫苗尚未可用，模型中未考虑疫苗接种情况。
本研究有助于确定降低病毒传播风险的措施，从而在室内空间提供更高的安全性。
