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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.

This study evaluates the differences between bioinformatics pipelines by analyzing samples collected from various built environments. Previous comparative studies of microbial community analysis pipelines have largely focused on bacterial communities, mock communities, or soil fungi, often with small sample sizes, and have not specifically targeted built environments. Our results highlight key differences between OTU (QIIME1) and ASV (QIIME2) analyses. OTU analysis clusters OTUs at 97% similarity and tends to show higher diversity values in diversity analyses. Regarding abundantly detected fungi, OTU analysis identified more genera than ASV analysis. However, the OTU method has a high rate of false positives and false negatives, indicating low error-removal capability and suggesting that many fungal genera may have been detected. Therefore, a combined approach using OTU analysis combined with ASV analysis allows for both the comprehensive detection of dominant taxa and the inclusion of rare species. Overall, our findings emphasize that the choice of pipeline significantly influences the composition of the observed fungal community in built environments. Careful consideration of both OTU and ASV strategies can enhance the reliability and completeness of fungal metabarcoding studies, particularly when studying complex indoor microbial communities.

HVAC systems have a significant impact on the indoor environment, and microbial contamination in HVAC systems has a significant effect on the indoor air quality. In this study, to gain a better understanding of the microbial contamination inside ACs, we used NGS to analyze the 16S rRNA gene of bacteria adhering to AC filters, cooling coils, fans, and air outlet surfaces. The five phyla in terms of the highest relative abundance were Proteobacteria, Firmicutes, Actinobacteria, Cyanobacteria, and Bacteroidetes. The surface of an AC filter provides a history of indoor airborne bacterial contamination, and of the 10 bacterial genera we detected with the highest abundance (in the following order: Pseudomonas > Staphylococcus > Paracoccus > Corynebacterium > Acinetobacter > Streptococcus > Methylobacterium > Enhydrobacter > Sphingomonas > Actinotignum) on the filter surface, the top 6 genera were Gram-negative bacteria. Furthermore, the seventh-most abundant genus adhering to the filter surface (Methylobacterium) was the second-most abundant genus on the cooling coil and fan, and the ninth-most abundant genus on the air filter (Sphingomonas) was the third-most abundant genus on the cooling coil. Various factors impact the bacterial flora inside AC units, including the location of the house, AC unit usage, and occupant activity.

Background. Allergic fungal airway diseases, such as asthma and allergic bronchopulmonary mycosis (ABPM), are often difficult to manage with medical treatment alone; therefore, environmental fungal exposure should be accurately evaluated and minimized. In the present study, we established a method to evaluate and eliminate fungal contamination in household air conditioners (ACs). Methods. In the fall of 2020, an environmental survey of living rooms was conducted in 17 Japanese residences of patients with ABPM or related diseases. Household ductless minisplit AC units were disassembled to collect swab samples from the internal parts (filter, heat exchanger, blower fan, and air vent), followed by high-pressure washing. Fungal abundance and composition in swab samples and cleaning effluents of ACs as well as house dust and air samples were determined using quantitative PCR and next-generation sequencing of the internal transcribed spacer 1 region, respectively. A weighted UniFrac distance was calculated to analyze the similarity of the mycobiome among the samples. Results. All interior parts of ACs contained high levels of fungal DNA, with the blower fans being the most contaminated parts. Cladosporium and Toxicocladosporium, followed by Aureobasidium, Aspergillus, and Rhodotorula, were the most common fungi detected in the AC unit. High-pressure washing decreased fungal abundance by over 99% in all AC parts. Fungal abundance and composition in blower fans were strongly correlated with those in cleaning effluents. Conclusion. Interior parts downstream of heat exchangers in household ACs are the major sites of fungal contamination, possibly polluting the indoor air in the residences. High-pressure washing is highly effective for decontamination.

In this study, we first conducted laboratory experiments on the sensitivity of a newly developed bioaerosol sensor (BAS) suitable for in situ measurements. Then, we performed an in situ test in a shared student space at a university. Furthermore, the effectiveness of ventilation and air purification as a mitigation measure for a location with high concentrations of bioaerosol particles (hot spots) was verified. The experimental results show that the measured values for polystyrene latex are in good agreement with the predicted Mie theory value. They also show a good response to fluorescent particles. The in situ test showed that the BAS fluorescent system does not respond to non-fluorescent particles but only to fluorescent particles. During respiratory infection outbreaks, real-time detection at hot spots and a reduction in particulate matter, including bioaerosols, through ventilation and air purification equipment are effective. In this study, the BAS measurement results showed significant correlations not only with fluorescent particles but also with live bacteria. This does not prove that viruses can be measured in real time. If real-time measurements for viruses become available in the future, the findings of this study will be helpful in mitigating respiratory tract infections caused by viruses.

Background Psychosocial and environmental factors at the workplace play a significant role in building-related symptoms (BRSs). Environmental factors change during summer cooling and winter heating using air-conditioning systems. Thus, significant risk factors in each season need to be clarified. Methods A nationwide cross-sectional study was conducted during summer in Japan and seasonal differences between summer and winter were evaluated. Self-administered questionnaires were distributed to 489 offices. Possible risk factors for BRSs associated with the work environment, indoor air quality, and job stressors were examined by multiple regression analyses. Results Among people having at least one BRS, the prevalence of BRSs in summer (27.8%) was slightly higher than that in winter (24.9%). High prevalence was observed for eye and nasal symptoms related to dryness and general symptoms related to psychological distress in both seasons. Analyses revealed that dryness of air was an important and significant risk factor associated with BRSs, and job stressors were significantly associated with general symptoms in both seasons. Conversely, humidity was a significant risk factor of general symptoms in summer (odds ratio, 1.20; 95% confidence interval, 1.02–1.43). Carpeting, recently painted walls, and unpleasant chemical odors in summer and noise, dust and dirt, and unpleasant odors such as body or food odors in both seasons were significant risk factors for BRSs. Conclusions Improvements in the physical environmental qualities in an office throughout the year are important along with the reduction in psychological distress related to work.

It is still undetermined if the main infection route of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), the virus that leads to coronavirus disease 2019 (COVID‐19), is infection through droplet, contact, or airborne transmission. However, confined spaces with poor ventilation are cited as a risk factor for group outbreaks, and there is growing interest in the effects of intervention through the appropriate operation of air‐conditioning and sanitary equipment to reduce the risk of airborne transmission. This study first offers an outline of the characteristics of the novel coronavirus disease and the cluster outbreak case reports that have been clarified until now. Subsequently, we describe the appropriate operating conditions for building equipment that are effective in reducing the risk of infection and also highlight specificities for each building use based on the guidance provided by healthcare institutions and with reference to the standard recommendations by Western academic societies related to building equipment.

The importance of effective ventilation as one of the measures against COVID-19 is widely recognized worldwide. In Japan, at the early stage of the pandemic, in March 2020, an official announcement was made about basic ventilation measures against COVID-19. WHO also used the term “long-range aerosol or long-range airborne transmission” for the first time in December 2021. Based on the aerosol infection control measures before 2021 by the Japanese government, we conducted experiments on methods related to partition placement as an element of effective ventilation methods. In July 2022, the governmental subcommittee on Novel Coronavirus Disease Control provided an emergent proposal about effective ventilation methods to prevent two types of aerosol infection; infection by large aerosol on the air current and infection by small floating aerosol diffusion in a room. They also showed the way of setting droplet prevention partitions, which do not block off ventilation based on this investigation’s results.

The human behavior has much impact on the infectious desease spreading. The pathogen generation is not uniform for the residential area since the human have some preference on where to be. The purpose of the present study is to evaluate the impact of the human preference on the seat choice behavior on the pathogen concentration. The preference of the seat selections in a train was modelled and the agent simulation was performed in order to evaluate the non-uniformity of pathogen. The concentration was calculated with Wells-Riley model. The results of the agent simulation showed the preference of seat choice based on the experimental results in a train environment. The seats at the end were more selected than other seats. The concentration at the seats at the end kept increasing because the agent sat there by turns and that is why there was no recovery time. The double effect of the more seat selection and the less recovery time has much impact on the non-uniformity of the concentration.

Subterranean temperature at a depth of 10 m is almost equal to the average outdoor air temperature of the same area. Therefore, if a building cooling trench is used as an outdoor air duct, outdoor air can be cooled in summer and warmed in winter. This energy-saving technique is often used in Japan. However, since the relative humidity in a cooling trench is high, microbe numbers tend to increase in summer. The present study sought to characterize the microbiome status in the cooling trench of such an office building in Japan. Specifically, we performed a metagenomic analysis in which we analyzed DNA directly upon collection from the environment, without intervening cultivation. The results showed the presence of bacteria of the genera Pseudomonas, Lactobacillus, Nesterenkonia, Staphylococcus, Deinococcus, Acinetobacter, Enhydorobacter , and Corynebacterium . Bacteria of the genera Nesterenkonia, Deinococcus, Enhydorobacter , and Corynebacterium predominated on the surface of the trench. Notably, bacteria of the genus Nesterenkonia constituted >50% of the organisms on the surface of the downstream end of the cooling trench. Principal coordinate analysis was used to compare bacterial inhabitants of outdoor air, indoor air from 2nd- and 3rdfloor offices, and the region downstream of the cooling trench. The results suggested that the microbiome of air in this cooling trench influenced indoor air within the building.