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Background Since the onset of the coronavirus disease-2019 (COVID-19) pandemic, the prevalence of respiratory infectious diseases, particularly, the flu epidemic, has considerably decreased. The low detection rate and decreased number of specimens have hindered the implementation of the Korea Influenza and Respiratory Viruses Surveillance System (KINRESS), a sentinel surveillance system. Most patients with influenza-like illness visit the COVID-19 screening clinic; therefore, the number of samples collected in sentinel surveillance has decreased by more than 50%. Thus, the Korea Disease Control and Prevention Agency supplemented sentinel surveillance with non-sentinel surveillance by private medical diagnostic centers. We report here a delayed and unprecedented high detection of human parainfluenza virus (hPIV) in the Republic of Korea during the COVID-19 pandemic through sentinel and non-sentinel surveillance. We also examined the causes and implications of the changes in prevalence of hPIV.l Methods We collected data for 56,984 and 257,217 samples obtained through sentinel and non-sentinel surveillance, respectively. Eight viruses were confirmed using real-time reverse transcription-polymerase chain reaction (PCR) or real-time PCR. Some specimens from the sentinel surveillance were used for genetic characterization of hPIV type 3. Results In 2020, hPIV was rarely detected; however, it was detected in August 2021. The detection rate continued to increase considerably in September and reached over 70% in October, 2021. The detection rate of hPIV3 was significantly higher in infants and preschoolers aged 0–6 years in both sentinel and non-sentinel surveillance. Detection of hPIV was delayed in metropolitan areas compared to that in suburban regions. The hemagglutinin-neuraminidase sequences of hPIV3 generated in 2021 were not distinct from those detected prior to the COVID-19 pandemic. Conclusions The operation of non-sentinel and sentinel surveillance to monitor respiratory viruses could sensitively detect an unprecedented revival of hPIV in the Republic of Korea during the COVID-19 pandemic.

The air pollution level of particulate matters in subway tunnel environments is severe. The present study conducted experimental measurements and analyses on dust-collection efficiencies and ozone emission rates in a lab-scale wind tunnel to determine a high-voltage electrode shape suitable for an electrostatic precipitator to remove airborne particles in subway tunnels. Six high-voltage electrode shapes (saw-type, few-saw-type, short-saw-type, tree-type, wave-type, and spike-type) were tested. The results indicate that while breakdown voltage of the spike-type high-voltage electrode was 66 % of other electrode shapes, its dust-collection efficiency per unit voltage was similar to that of other electrode shapes. However, the dust-collection efficiency per unit of power in the spike-type high-voltage electrode was significantly low. Moreover, the wave-type high-voltage electrode shape had 20 % lower dust-collection efficiency than the saw-type and tree-type high-voltage electrode shapes under conditions of low voltage and high flow velocities. Ozone emission rates for all shapes increased proportionally to the electric current. However, ozone emission rates for each high-voltage electrode shape are varied as 12–23 μg/s per mA. The saw-type and tree-type high-voltage electrode shapes were superior in terms of dust collection, 90 % collection efficiency was shown at about 1.5 W/(m/s)2. The saw-type had a lower ozone emission rate (16.4 μg/s per mA) than the tree-type (19.6 μg/s per mA). Thus, the saw-type shape was the most suitable as a high-voltage electrode in the electrostatic precipitator for removing airborne particles in a subway. The results also indicate that both dust-collection efficiencies and ozone emission rates should be evaluated concurrently when evaluating electrostatic precipitator high-voltage electrodes.

A real-time reverse transcription polymerase chain reaction (RT-qPCR) assay that does not require Emergency Use Authorization (EUA) reagents was tested and validated for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the early stages of the outbreak of coronavirus disease 2019 (COVID-19) in the Republic of Korea. Early diagnosis of COVID-19 enables timely treatment and the implementation of public health measures. We validated the sensitivity, specificity, precision, linearity, accuracy, and robustness of the RT-qPCR assay for SARS-CoV-2 detection and compared its performance with that of several EUA-approved kits. Our RT-qPCR assay was highly specific for SARS-CoV-2 as demonstrated by not amplifying 13 other viruses that cause respiratory diseases. The assay showed high linearity using a viral isolate from a patient with known COVID-19 as well as plasmids containing target SARS-CoV-2 genes as templates. The assay showed good repeatability and reproducibility with a coefficient of variation of 3%, and a SARS-CoV-2 limit of detection of 1 PFU/mL. The RT-qPCR-based assay is highly effective and can facilitate the early diagnosis of COVID-19 without the use of EUA-approved kits or reagents in the Republic of Korea.

A large amount of fine dust containing iron (Fe) components is scattered by the movement of trains through a subway tunnel. The fine dust spreads to the subway platforms where they are inhaled by passengers, leading to a possibility of acquiring respiratory disease. In this study, a baffle dust collector, which is a type of inertial dust collector, was considered to be attached to the bottom of a train traveling through a Gwangju city subway tunnel to collect dispersed dust particles. To assure a certain level of air suction, a powered fan was installed at the back of the baffle dust collector, which comprised 12 parallel particle-attracting plates connected to perforated circular particle- collecting tubes. The air flow around the baffle dust collector was analyzed, and the volume of air flowing into the collector was predicted with respect to the train speed. Particle analysis was also used to predict the dust collection efficiency in the uniform-speed section of the subway tunnel where the train travelled at a constant speed of 70 km/h, and the results were compared with wind tunnel measurements. It was found that the air flow rate into the baffle dust collector at the constant train speed of 70 km/h was only approximately 2.1 % higher than that in the low-speed section of the tunnel where the train moved at a speed of about 10 km/h. In addition, the cutoff size of the suctioned particles at a speed of 70 km/h was determined to be 7.8 μm.

Understanding characteristics of diurnal particle concentration variation in an underground subway tunnel is important to reduce subway passengers’ exposure to high levels of toxic particle pollution. In this study, real-time particle monitoring for eight consecutive days was done at a shelter located in the middle of a one-way underground subway tunnel in Seoul, Republic of Korea, during the summer of 2015. Particle mass concentration was measured using a dust monitor and particle number concentration using an optical particle counter. From the diurnal variations in PM10, PM2.5, and PM1, concentrations of particles larger than 0.54 μm optical particle diameter were affected by train frequency whereas those of particles smaller than 0.54 μm optical particle diameter were not changed by train frequency. Number concentration of particles smaller than 1.15 μm optical particle diameter was dependent on outdoor ambient air particle concentration level, whereas that of particles larger than 1.15 μm optical particle diameter was independent of outdoor ambient air due to low ventilation system transmission efficiency of micrometer-sized particles. In addition, an equation was suggested to predict the diurnal particle concentration in an underground tunnel by considering emission, ventilation, and deposition effects.

The Gaussian Diffusion Sphere Model (GDSM) was developed and improved to predict the particle deposition velocity onto a flat plate exposed to parallel airflow by considering thermophoresis in addition to the Brownian diffusion and the gravitational settling of particles. The plate surface temperature was varied and considered to be either hotter or colder than the temperature of the parallel airflow. The GDSM was able to estimate the particle deposition velocity under the influence of thermophoresis not only correctly but also very quickly, compared to the numerical approach to calculate the deposition velocity by simulating thermo-flow and particle transport. As the next step, the particle deposition velocities onto both face-up and face-down surfaces of the 450 mm wafer exposed to the parallel airflow were predicted with the GDSM by varying the wafer temperature. It was anticipated that the schemes of heating the wafer and placing the critical surface inverted during the horizontal transport of the wafer could greatly reduce the particulate contamination of the wafer critical surface.