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.

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.

Drive-Through Screening Center for COVID-19: a Safe and Efficient Screening System against Massive Community Outbreak.

As the coronavirus disease 2019 (COVID-19) outbreak is ongoing, the number of individuals to be tested for COVID-19 is rapidly increasing. For safe and efficient screening for COVID-19, drive-through (DT) screening centers have been designed and implemented in Korea. Herein, we present the overall concept, advantages, and limitations of the COVID-19 DT screening centers. The steps of the DT centers include registration, examination, specimen collection, and instructions. The entire service takes about 10 minutes for one testee without leaving his or her cars. Increased testing capacity over 100 tests per day and prevention of cross-infection between testees in the waiting space are the major advantages, while protection of staff from the outdoor atmosphere is challenging. It could be implemented in other countries to cope with the global COVID-19 outbreak and transformed according to their own situations.

Extensive Viable Middle East Respiratory Syndrome (MERS) Coronavirus Contamination in Air and Surrounding Environment in MERS Isolation Wards.

BACKGROUND: The largest outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV) outside the Middle East occurred in South Korea in 2015 and resulted in 186 laboratory-confirmed infections, including 36 (19%) deaths. Some hospitals were considered epicenters of infection and voluntarily shut down most of their operations after nearly half of all transmissions occurred in hospital settings. However, the ways that MERS-CoV is transmitted in healthcare settings are not well defined. METHODS: We explored the possible contribution of contaminated hospital air and surfaces to MERS transmission by collecting air and swabbing environmental surfaces in 2 hospitals treating MERS-CoV patients. The samples were tested by viral culture with reverse transcription polymerase chain reaction (RT-PCR) and immunofluorescence assay (IFA) using MERS-CoV Spike antibody, and electron microscopy (EM). RESULTS: The presence of MERS-CoV was confirmed by RT-PCR of viral cultures of 4 of 7 air samples from 2 patients' rooms, 1 patient's restroom, and 1 common corridor. In addition, MERS-CoV was detected in 15 of 68 surface swabs by viral cultures. IFA on the cultures of the air and swab samples revealed the presence of MERS-CoV. EM images also revealed intact particles of MERS-CoV in viral cultures of the air and swab samples. CONCLUSIONS: These data provide experimental evidence for extensive viable MERS-CoV contamination of the air and surrounding materials in MERS outbreak units. Thus, our findings call for epidemiologic investigation of the possible scenarios for contact and airborne transmission, and raise concern regarding the adequacy of current infection control procedures.

Analysis of Infection Transmission Routes through Exhaled Breath and Cough Particle Dispersion in a General Hospital.

Identifying infection transmission routes in hospitals may prevent the spread of respiratory viruses and mass infections. Most previous related research focused on the air movement of passive tracers, which typically represent breathing. In this study, particle evaporation and dispersions with various particle sizes were applied to evaluate particle movement because of breathing and coughing using computational fluid dynamics (CFD) simulations. Pyeongtaek St. Mary Hospital, where a Middle East respiratory syndrome (MERS) index patient infected several patients on the same floor, was used for a case study. We compared the dispersion characteristics of various particle sizes and validated results by comparing infection rates in different ward. Results indicated that droplets spread across the corridor and dispersed to wards that were more than 17 m apart from the index patient by natural ventilation. Droplets from exhaled breath under steady-state simulation showed a wider range of dispersion than cough droplets under transient simulation, but cough droplet dispersion was more consistent with the actual infection rate in each ward. Cough droplets sized under 75 µm evaporated to 26% of the initial size and started to disperse into the corridor within one minute; in nine minutes, droplets dispersed throughout every ward. This study may increase awareness on the dispersion characteristics of infectious particles.

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.

Estimating the germicidal effect of upper-room UVGI system on exhaled air of patients based on ventilation efficiency.

Upper room (UR)-ultraviolet germicidal (UVGI) systems, one of several disinfection applications of UV, target airborne infectious diseases in rooms of buildings such as healthcare facilities. Previous studies have introduced many experiments showing the germicidal effect of UR-UVGI systems. In this study, a novel numerical method of estimating the germicidal effect of UR-UVGI systems for air exhaled by ward patients was introduced. The method adopts and modifies the concept of ventilation efficiency because the germicidal effect depends upon how the air containing airborne infectious particles flows and stays within UV-radiated area. A case study based on a four-patient ward showed that UV doses were correlated with the age of the air exhaled by a source patient, as expected. Moreover, the UV doses were considerably affected by the position of the UR-UVGI system. Inactivation rates of the influenza virus estimated using the UV doses, were in the range of 48-74%, and those of Mycobacterium tuberculosis were 68-90% in the breathing area of a neighboring patient. The results indicate not directly the decreased concentration of airborne infectious particles, but the possibility of inactivation caused by the UR-UVGI system, which is useful for system optimization.

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.

Airflow analysis of Pyeongtaek St Mary's Hospital during hospitalization of the first Middle East respiratory syndrome patient in Korea.

Middle East respiratory syndrome (MERS) is known to be transmitted through close contact. However, epidemiological surveys of MERS in Korea indicated that some secondary patients were infected without close contact. Therefore, the possibility of other transmission routes must be identified. In this study, the possibility of MERS spreading through airflow was investigated on the eighth floor of Pyeongtaek St Mary's Hospital. Computational fluid dynamics was used to analyse the indoor airflow and passive tracer diffusion during the index patient's stay. Six cases were simulated for different outdoor wind directions and indoor mechanical ventilation operations. When a passive tracer was released in ward 8104, where the index patient was hospitalized, the passive tracer spread through the indoor airflow, which was created by the outdoor airflow. Ward 8109, which had the largest number of infected cases and was far distant from ward 8104, showed passive tracer concentration in all cases. This result indicates that MERS may have spread through airflow. The study results do not imply that the infection pathway of MERS is airborne. However, the results show the possibility of MERS spreading through airflow in specific environments such as poor ventilation environments.

Airflow as a Possible Transmission Route of Middle East Respiratory Syndrome at an Initial Outbreak Hospital in Korea.

In this study, the results of an airflow investigation conducted on 7 June 2015 as part of a series of epidemiologic investigations at Pyeongtaek St. Mary's Hospital, South Korea, were investigated. The study involved 38 individuals who were infected directly and indirectly with Middle East Respiratory Syndrome (MERS), by a super-spreader patient. Tracer gas experiments conducted on the eighth floor, where the initial patient was hospitalized, confirmed that the tracer gas spread to adjacent patient rooms and rooms across corridors. In particular, the experiment with an external wind direction and speed similar to those during the hospitalization of the initial patient revealed that the air change rate was 17⁻20 air changes per hour (ACH), with air introduced through the window in the room of the infected patient (room 8104). The tracer gas concentration of room 8110, which was the farthest room, was 7.56% of room 8104, indicating that a high concentration of gas has spread from room 8104 to rooms across the corridor. In contrast, the tracer gas was barely detected in a maternity ward to the south of room 8104, where there was no secondary infected patient. Moreover, MERS is known to spread mainly by droplets through close contact, but long-distance dispersion is probable in certain environments, such as that of a super-spreader patient hospitalized in a room without ventilation, hospitals with a central corridor type, and indoor airflow dispersion due to external wind.

A Study on the Contaminant Dispersion from Isolation Ward under Abnormal Operation of Facilities.

Due to the recent outbreaks of infectious diseases, such as severe acute respiratory syndrome (SARS), Influenza and Ebola, isolation facilities have played an important role to prevent infectious diseases from spreading at initial stage. An isolation ward is a facility to isolate patients physically and to care them safely. One way to isolate a patient physically is to build a negative pressure isolation facility. However, unexpected failure or misuse of such facility makes it difficult to maintain negative pressure and eventually causes secondary infection, leaking the infectious pathogen to outside of the isolation ward. This study identifies the amount and velocity of leakage air from a patient ward by tracer gas experiment under abnormal operations of an isolation facility. In addition, computational fluid dynamics (CFD) allowed us to observe the outflow mechanism of pollutant. The results show that abnormal operations of a facility spreads pathogens to neighboring areas immediately and timely actions should be prepared against them.

Epidemiologic features of the first MERS outbreak in Korea: focus on Pyeongtaek St. Mary's Hospital.

OBJECTIVES: This study investigated the epidemiologic features of the confirmed cases of Middle East Respiratory Syndrome (MERS) in Pyeongtaek St. Mary's Hospital, where the outbreak first began, in order to identify lessons relevant for the prevention and control of future outbreaks. METHODS: The patients' clinical symptoms and test results were collected from their medical records. The caregivers of patients were identified by phone calls. RESULTS: After patient zero (case #1) was admitted to Pyeongtaek St. Mary's Hospital (May 15-May 17), an outbreak occurred, with 36 cases between May 18 and June 4, 2015. Six patients died (fatality rate, 16.7%). Twenty-six cases occurred in the first-generation, and 10 in the second-generation. The median incubation period was five days, while the median period from symptom onset to death was 12.5 days. While the total attack rate was 3.9%, the attack rate among inpatients was 7.6%, and the inpatients on the eighth floor, where patient zero was hospitalized, had an 18.6% attack rate. In contrast, caregivers and medical staff showed attack rates of 3.3% and 1.1%, respectively. CONCLUSIONS: The attack rates were higher than those of the previous outbreaks in other countries. The outbreak spread beyond Pyeongtaek St. Mary's Hospital when four of the patients were moved to other hospitals without appropriate quarantine. The best method of preventing future outbreaks is to overcome the vulnerabilities observed in this outbreak, such as ward crowding, patient migration without appropriate data sharing, and the lack of an initial broad quarantine.