Estimation of Occupancy Using IoT Sensors and a Carbon Dioxide-Based Machine Learning Model with Ventilation System and Differential Pressure Data.

Infectious diseases such as the COVID-19 pandemic have necessitated preventive measures against the spread of indoor infections. There has been increasing interest in indoor air quality (IAQ) management. Air quality can be managed simply by alleviating the source of infection or pollution, but the person within a space can be the source of infection or pollution, thus necessitating an estimation of the exact number of people occupying the space. Generally, management plans for mitigating the spread of infections and maintaining the IAQ, such as ventilation, are based on the number of people occupying the space. In this study, carbon dioxide (CO2)-based machine learning was used to estimate the number of people occupying a space. For machine learning, the CO2 concentration, ventilation system operation status, and indoor-outdoor and indoor-corridor differential pressure data were used. In the random forest (RF) and artificial neural network (ANN) models, where the CO2 concentration and ventilation system operation modes were input, the accuracy was highest at 0.9102 and 0.9180, respectively. When the CO2 concentration and differential pressure data were included, the accuracy was lowest at 0.8916 and 0.8936, respectively. Future differential pressure data will be associated with the change in the CO2 concentration to increase the accuracy of occupancy estimation.

The Wavelength-Based Inactivation Effects of a Light-Emitting Diode Module on Indoor Microorganisms.

With the increased incidence of infectious disease outbreaks in recent years such as the COVID-19 pandemic, related research is being conducted on the need to prevent their spread; it is also necessary to develop more general physical-chemical control methods to manage them. Consequently, research has been carried out on light-emitting diodes (LEDs) as an effective means of light sterilization. In this study, the sterilization effects on four types of representative bacteria and mold that occur indoors, Bacillus subtilis, Escherichia coli, Penicillium chrysogenum, and Cladosporium cladosporidides, were confirmed using LED modules (with wavelengths of 275, 370, 385, and 405 nm). Additionally, power consumption was compared by calculating the time required for 99.9% sterilization of each microorganism. The results showed that the sterilization effect was high, in the order 275, 370, 385, and 405 nm. The sterilization effects at 385 and 405 nm were observed to be similar. Furthermore, when comparing the power consumption required for 99.9% sterilization of each microorganism, the 275 nm LED module required significantly less power than those of other wavelengths. However, at 405 nm, the power consumption required for 99.9% sterilization was less than that at 370 nm; that is, it was more efficient and similar to or less than that at 385 nm. Additionally, because 405 nm can be applied as general lighting, it was considered to have wider applicability and utility compared with UV wavelengths. Consequently, it should be possible to respond to infectious diseases in the environment using LEDs with visible light wavelengths.

Inactivation of airborne microbial contaminants by a heat-pump-driven liquid-desiccant air-conditioning system

The COVID-19 pandemic has led to increasing interest in controlling airborne virus transmission during the operation of air-conditioning systems. Therefore, beyond an examination of the ability of liquid-desiccant material itself to inactivate microbes, a heat-pump-driven liquid-desiccant air-conditioning system was proposed and constructed to experimentally investigate the effect of liquid-desiccant solution on the inactivation of airborne bacteria and fungi in various air-conditioning processes. The proposed system comprises a liquid-desiccant unit to dehumidify or humidify process air using a desiccant-solution and heat-pump unit to cool or heat it and accommodate solution thermal loads. The decrease in the concentration of airborne bacteria and fungi before and after passing through the system (i.e., inactivation efficiency) were compared for the base, summer, and winter operating modes. The results indicated that airborne fungi were less inactivated than bacteria because they possess more stress-resistant cellular structures that resist inactivation. During the air-conditioning processes in both the summer and winter operating modes, the bacterial and fungal inactivation efficiencies improved compared to the base mode owing to the contact with desiccant solution. The higher solution flow rate and solution temperature improved the bacterial inactivation efficiency by 27% for the winter compared to the summer mode. Conversely, because of possible growth of fungi in the heated and humidified supply air in the winter, the fungal inactivation efficiency improved by only 1.5% for the winter compared to the summer mode. In conclusion, the proposed system can contribute to control the airborne transmission of microbial contaminants while operating air-conditioning systems.

COVID-19 Cluster Linked to Aerosol Transmission of SARS-CoV-2 via Floor Drains.

BACKGROUND: Recently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission through exposure to aerosols has been suggested. Therefore, we investigated the possibility of aerosol SARS-CoV-2 transmission within an apartment complex where residents reported testing positive for SARS-CoV-2 despite having no direct contact with other SARS-CoV-2-infected people. METHODS: Information on symptom onset and exposure history of the patients was collected by global positioning system (GPS) tracking to investigate possible points of contact or spread. Samples collected from patients and from various areas of the complex were analyzed using RNA sequencing. Phylogenetic analysis was also performed. RESULTS: Of 19 people with confirmed SARS-CoV-2 infection, 5 reported no direct contact with other residents and were from apartments in the same vertical line. Eight environmental samples tested positive for the virus. Phylogenetic analyses revealed that 3 of the positive cases and 1 environmental sample belonged to the B.1.497 lineage. Additionally, 3 clinical specimens and 1 environmental sample from each floor of the complex had the same amino acid substitution in the ORF1ab region. CONCLUSIONS: SARS-CoV-2 transmission possibly occurs between different floors of an apartment building through aerosol transmission via nonfunctioning drain traps.

Nosocomial Outbreak of COVID-19 in a Hematologic Ward.

BACKGROUND: Coronavirus disease 2019 (COVID-19) outbreaks occur in hospitals in many parts of the world. In hospital settings, the possibility of airborne transmission needs to be investigated thoroughly. MATERIALS AND METHODS: There was a nosocomial outbreak of COVID-19 in a hematologic ward in a tertiary hospital, Seoul, Korea. We found 11 patients and guardians with COVID-19 through vigorous contact tracing and closed-circuit television monitoring. We found one patient who probably had acquired COVID-19 through airborne-transmission. We performed airflow investigation with simulation software, whole-genome sequencing of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). RESULTS: Of the nine individuals with COVID-19 who had been in the hematologic ward, six stayed in one multi-patient room (Room 36), and other three stayed in different rooms (Room 1, 34, 35). Guardian in room 35 was close contact to cases in room 36, and patient in room 34 used the shared bathroom for teeth brushing 40 minutes after index used. Airflow simulation revealed that air was spread from the bathroom to the adjacent room 1 while patient in room 1 did not used the shared bathroom. Airflow was associated with poor ventilation in shared bathroom due to dysfunctioning air-exhaust, grill on the door of shared bathroom and the unintended negative pressure of adjacent room. CONCLUSION: Transmission of SARS-CoV-2 in the hematologic ward occurred rapidly in the multi-patient room and shared bathroom settings. In addition, there was a case of possible airborne transmission due to unexpected airflow.

Effectiveness of surgical, KF94, and N95 respirator masks in blocking SARS-CoV-2: a controlled comparison in 7 patients.

BACKGROUND: Data on the filtration efficacies of various masks against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are limited. We thus evaluate the effectiveness of the surgical mask, the N95 respirator mask, and its equivalent (KF94 mask) in filtering SARS-CoV-2. METHODS: Patients hospitalised with SARS-CoV-2 infection were instructed to cough five times each while wearing (1) no mask, (2) surgical mask, (3) KF94 mask, and (4) N95 mask. The coughs were separated by 20-second intervals, and the patients were rested for at least 5 min between each setting. SARS-CoV-2 viral loads in patient samples (i.e. nasopharyngeal swabs and saliva), petri dishes placed in front of the patients during coughing, and swabs from the outer and inner surfaces of the masks were analysed with PCR. RESULTS: A total of 7 patients with SARS-CoV-2 infection participated in the mask test. SARS-CoV-2 was detected on the petri dishes after coughing in 3 out of 7 cases with the surgical mask or no mask. Viral particles were not found in the petri dishes after coughing while wearing the N95 mask or the KF94 mask. While viral particles were detected in both the inner and outer surfaces of the surgical masks, those were detected only in the inner surfaces of the N95 and K94 masks. CONCLUSION: Surgical masks were less effective in filtering viral particles from coughing patients with SARS-CoV-2 infection. N95 masks and its equivalents efficiently blocked SARS-CoV-2 particles from coughing patients.