Quantity, Size Distribution and Behavior Characteristics of Cough-generated Aerosol Produced by Cold Patients
감기 환자의 호흡기에서 발생하는 에어로졸의 특성

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보건대학원 환경보건학과
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서울대학교 대학원
Cough aerosolairborne transmissionrespiratory infectionsdisease transmissiondroplet nuclei
학위논문 (석사)-- 서울대학교 대학원 : 환경보건학과, 2017. 2. 윤충식.
It is generally recognized that most nosocomial infections are spread by expelled particles at close range, usually within 1-m from the site of generation, and occasionally through contact. Although the World Health Organization (WHO) established a cut-off to classify droplets (> 5 μm) and airborne particles (< 5 μm), and a 2 m cut-off for patients during the Middle East respiratory syndrome outbreak in Korea in 2015, questions have been raised regarding the efficacy of a single cut-off delineation and possible infection by aerosol transmission beyond a distance of 2 m. The purpose of this study was to characterize cough-generated aerosol emissions from cold patients, and to determine their behavioral characteristics (particle transmission distance) in indoor air.

This study was carried out with 10 subjects who were diagnosed with acute upper respiratory infections at medical institutions. Patients participated in two experiments. The first experiment was conducted using a stainless steel chamber and the second was conducted in a clean room. The number and size distribution of particles generated from each cough were measured in the stainless steel chamber. Tests were repeated three times by each patient. In the clean room, participants coughed and total particle concentration before, during, and after the cough was measured once for each patient at 0.5 m and 3 m. A scanning mobility particle sizer and an optical particle spectrometer were used to measure the particles, and an ultrasonic spirometer was used to measure pulmonary function of the lungs, mean cough aerosol volume, and peak airflow during coughing. All measurements were performed in the same way after patients recovered and differences between infections were compared.

The number of particles from a cough by participants with a cold increased by 560 ± 513% compared to those after recovery (while ill: 4,995,000 ± 6,090,000, after recovery: 1,376,000 ± 1,459,000) (p < 0.001). The proportion of expelled particles with a diameter < 5 μm (particles that can be transmitted through the air) was 99.9 ± 0.3% of the total number and 90.2 ± 12.2% of total surface area while the subjects had a cold. Most of the particles propagated to the far field (3 m) and the near field (0.5 m) in the air, regardless of the subjects infection status. The number of particles was significantly higher (p < 0.001) than the background concentration when the patient was coughing even in the far field, which exceeded the WHO recommended isolation distance of 2 m.

The results show that the number of aerosol particles expelled during coughing by patients with a cold was significantly higher (p < 0.001) than that after recovery from a cold. We confirmed that aerosols generated during coughing, regardless of symptoms, were transferred to the far field (3 m) and near field (0.5 m). These results suggest that the < 5 μm dichotomous cut-off for a droplet and aerosol criterion of the WHO, and the 2 m cut-off for possible airborne infection of the Korea Centers for Disease Control, should be reconsidered for effective prevention of airborne infections.
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Graduate School of Public Health (보건대학원)Dept. of Environmental Health (환경보건학과)Theses (Master's Degree_환경보건학과)
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