Abstract
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a new zoonotic agent that emerged in December 2019, causes coronavirus disease 2019 (COVID-19). This infection can be spread by asymptomatic, presymptomatic, and symptomatic carriers. SARS-CoV-2 spreads primarily via respiratory droplets during close person-to-person contact in a closed space, especially a building. This article summarizes the environmental factors involved in SARS-CoV-2 transmission, including a strategy to prevent SARS-CoV-2 transmission in a building environment. SARS-CoV-2 can persist on surfaces of fomites for at least 3 days depending on the conditions. If SARS-CoV-2 is aerosolized intentionally, it is stable for at least several hours. SARS-CoV-2 is inactivated rapidly on surfaces with sunlight. Close-contact aerosol transmission through smaller aerosolized particles is likely to be combined with respiratory droplets and contact transmission in a confined, crowded, and poorly ventilated indoor environment, as suggested by some cluster cases. Although evidence of the effect of aerosol transmission is limited and uncertainty remains, adequate preventive measures to control indoor environmental quality are required, based on a precautionary approach, because COVID-19 has caused serious global damages to public health, community, and the social economy. The expert panel for COVID-19 in Japan has focused on the “3 Cs,” namely, “closed spaces with poor ventilation,” “crowded spaces with many people,” and “close contact.” In addition, the Ministry of Health, Labour and Welfare of Japan has been recommending adequate ventilation in all closed spaces in accordance with the existing standards of the Law for Maintenance of Sanitation in Buildings as one of the initial political actions to prevent the spread of COVID-19. However, specific standards for indoor environmental quality control have not been recommended and many scientific uncertainties remain regarding the infection dynamics and mode of SARS-CoV-2 transmission in closed indoor spaces. Further research and evaluation are required regarding the effect and role of indoor environmental quality control, especially ventilation.
Highlights
In late December 2019, a cluster of severe pneumonia cases emerged in humans in Wuhan, Hubei Province, China [1, 2]
As most people spend more than 90% of their daily lives inside buildings, it is essential to understand the potential transmission dynamics of SARS-CoV-2 inside a building, the spatial dynamics, and the building operational factors that potentially promote and mitigate the transmission of SARS-CoV-2 and the spread of COVID-19
At room temperature (24 °C), the virus half-life ranged from 6.3 to 18.6 h depending on the relative humidity but was reduced to 1.0–8.9 h when the temperature was increased to 35 °C [39]. These findings suggest that a potential for fomite transmission may persist for hours to days in indoor environments and that the survivability of fomites is affected by temperature and relative humidity, as well as by the presence of protein found in human sputum
Summary
In late December 2019, a cluster of severe pneumonia cases emerged in humans in Wuhan, Hubei Province, China [1, 2]. The causative pathogen was identified as a novel coronavirus that was named the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [3, 4]. The disease rapidly spread internationally, raising global public health concerns, and was subsequently termed coronavirus disease 19 (COVID-19) [5, 6]. The most common clinical manifestations of patients with COVID-19 are fever, cough, shortness of breath, and fatigue. Some patients have shown radiographic ground-glass lung changes and eventually died of acute respiratory distress syndrome (ARDS) [7, 8]. The World Health Organization (WHO) declared COVID-19 as a global pandemic on March 11, 2020 [9]
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