The World Health Organization considered the widespread of COVID-19 over the world as a pandemic. There is still a lack of understanding of its origin, transmission, and treatment methods. Understanding the influencing factors of the COVID-19 can help mitigate its spread, but little research on the spatial factors has been conducted. Therefore, this study explores the effects of urban geometry and socio-demographic factors on the COVID-19 cases in Hong Kong. For each patient, the places they visited during the incubation period before going to hospital were identified, and matched with corresponding attributes of urban geometry (i.e., building geometry, road network, greenspace) and socio-demographic factors (i.e., demographic, educational, economic, household and housing characteristics) based on the coordinates. The local cases were then compared with the imported cases using the stepwise logistic regression, the logistic regression with case-control of time, and the least absolute shrinkage and selection operator regression to identify factors influencing local disease transmission. Results show that the building geometry, road network and certain socio-economic characteristics are significantly associated with COVID-19 cases. In addition, the results indicate that urban geometry is playing a more important role than the socio-demographic characteristics in affecting the COVID-19 incidences. These findings provide a useful reference to the government and the general public as to the spatial vulnerability of the COVID-19 transmission and to take appropriate preventive measures in high-risk areas.

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Occupational Exposure to Volatile Organic Compounds and Mitigation by Local Exhaust Ventilation in Printing Plants: Michael K.H. LEUNG et al. The University of Hong Kong, HongKong-The extensive use of multiple organic solvents in offset lithographic printing causing high emissions of volatile organic compounds (VOCs) indeed poses a serious risk to printing workers' health. In this study, indoor air quality (IAQ) assessments were carried out in seven printing plants and the main objectives were to understand the effect of VOC emissions on IAQ and develop effective mitigation measures to protect workers. The thorough gas chromatography/mass spectrometry (GC/MS) measurements showed that although a variety of VOCs were presented in the indoor air, none of them was found close to individual 8-h timeweighted average (TWA) of the occupational exposure limit (OEL). The additive effect was also found below the critical value of unity. However, short-term personal exposure to total volatile organic compounds (TVOCs) was exceedingly high when a print worker carried out blanket and ink roller cleaning procedures. Therefore, the occupational health risk was mainly due to repeated short-term exposures during intermittent VOC-emitting procedures rather than long-term exposure to background VOCs. Push-pull local exhaust ventilation (LEV) was identified as an effective mitigation measure. Computational fluid dynamics (CFD) analysis was conducted to study the push-pull LEV operation. It was found that there existed a threshold LEV air flow rate for an abrupt reduction in the worker's exposure to VOCs. The reduction was less sensitive when the LEV airflow was further increased beyond the threshold. These phenomena, consistent with experimental results reported by other investigators, were explained by detailed CFD analysis showing the competition between the general ventilation and the push-pull LEV to become the dominating driving force for the resultant local flow pattern. (J Occup Health 2005; 47: 540-547)