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Relative effectiveness of ventilation in community indoor environmentsfor controlling infectionGao, Xiaolei., 高晓磊. January 2011 (has links)
The existence, probability and control measures of airborne infections
have been widely discussed for centuries. Although public belief regarding
airborne infection kept on altering throughout the entire history of medicine
and is still controversial, many airborne transmission experiments and airborne
infection outbreak analyses have been carried out. Different airborne
transmission models have been built and various airborne control measures
have been evaluated. One of the major knowledge gaps obstructing
applications of some airborne control measures in clinical practices and public
applications is that there is a lack of evidence in proving the effectiveness of
such measures.
Ventilation as an important airborne infection control method can be
achieved by opening windows, or increasing the outdoor air supply rate in
mechanical ventilation systems or indirectly by using filters and ultraviolet
equipments. However the applications of ventilation in infection control were
largely restricted to isolation rooms rather than regarded as a public control
measure. In this study we focus on evaluating the effectiveness of ventilation
as a community measure. Results, therefore, can provide evidence for using
ventilation as a public health measure for controlling respiratory diseases
transmitted by the airborne route or multi-routes.
Two mathematical modeling approaches (deterministic model and social
network model) are adopted to estimate different airborne diseases outbreaks
with a focus on ventilation and a corresponding analysis of their relative
effectiveness compared with other public health measures. A comprehensive
understanding of detailed control strategies (including both engineering and
public health control) will be achieved through gradually complicated and
realistic models.
It’s commonly believed that many respiratory infections are transmitted
through multiple routes including airborne, droplet-borne and contact routes.
Hence the effectiveness of airborne control measures was doubted when the
airborne route was not dominant. Therefore, we developed a model to simulate
partially airborne transmitted diseases outbreaks and evaluated the relative
effectiveness of ventilation when the role of airborne transmission altered.
Knowing the complex transmission mechanisms of respiratory
transmission and the role of the airborne route in the transmission process is
essential in determining the effectiveness of airborne control measures. Hence
in this study we also tested the virus exposures dose to infectious patients at
different distances when patients were carrying out different respiratory
activities. A complex model considering transmission mechanisms of
respiratory infections was also built to evaluate the influence of the
transmission route in large scale outbreak simulations.
The results showed that increasing ventilation rate especially in homes,
offices and classrooms is an effective control method for controlling airborne
and partially airborne transmitted infections. Combining isolation and
increasing ventilation rate can reach similar or even better control effect
compared with other general public health interventions such as vaccination.
This finding suggested the important role of ventilation in airborne infectious
disease prevention and intervention. The ventilation rate required by existing
ventilation standards such as ASHRAE 62 might be too low for the purpose of
controlling possible airborne outbreaks. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy
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The design of isolation ward for reducing airborne infection in common clinical settings. / 臨床環境條件下隔離病房設計以減少空氣傳播感染 / CUHK electronic theses & dissertations collection / Digital dissertation consortium / Lin chuang huan jing tiao jian xia ge li bing fang she ji yi jian shao kong qi chuan bo gan ranJanuary 2011 (has links)
According to recommendations from the Facility Guidelines Institute (FGI) of the American Institute of Architects (AIA), World Health Organization (WHO) and Center for Disease Control and Prevention (CDC), a common engineering approach to isolation room design is to maintain the air ventilation rate at a minimum of 12 air changes per hour (ACH) for mixing and dilution, and a negative pressure in the room to direct airflow inwards, instead of leaking outwards. / In collaborations with physicians in the Respiratory Division and the Intensive Care Unit (ICU) at the Chinese University of Hong Kong (CUHK), a series of experiments were carried out to verify the ventilation performance of an All room at the Princess Margaret Hospital (PMH). Experiments investigated the effects of ACH, the control of airflow direction, the air tightness of the automatic swing door and the application of positive pressure ventilation procedures, such as high flow rate oxygen masks, jet nebulizers and NPPV. These were extensively tested in two different isolation rooms of the Prince of Wales Hospital (PWH) and PMH, under common clinical circumstances and environmental conditions. / Many patients with severe respiratory infection require supportive therapy for respiratory failure. Common interventions involve supplemental oxygen to improve tissue oxygenation. In the worst scenario, mechanical ventilation via non-invasive positive pressure ventilation (NPPV) may be required. Since a large amount of aerosols is generated during these interventions, there is a great risk of spreading infectious aerosols from the respiratory tract of the patient to the surrounding environment. / The aerodynamic data in this thesis infonns architects and engineers on how to improve the hospital ward ventilation design so as to avoid aerosol and ventilation leakage. Ultimately, it is hoped that this work may play a role in preventing devastating nosocomial outbreaks in the future. / The design of airborne infection isolation (AII) room has become one of the major research domains following the emergence of the global concern of acute respiratory diseases in this century. These include severe acute respiratory syndrome (SARS) in 2003, H5N1 avian influenza, and pandemic influenza H1N1 in 2009. All of which have claimed thousands of lives. Even with the current stringent design and practice guidelines, nosocomial infection of healthcare workers (HCWs) and inpatients continues to occur. This implies that there might be limitations in current isolation ward designs. / The experiments implemented a high-fidelity human patient simulator (HPS) which could be programmed with different lung breathing conditions and oxygen flow rate settings. The patient exhaled air dispersion distances and airflow patterns were captured in detail with a non-intrusive, laser light sheet, smoke particle scattering technique, designed for this thesis. Thin laser light sheets were generated by a high energy YAG laser with custom cylindrical optics. Smoke concentration in the patient exhaled air and leakage jets was estimated from the intensity of light scattered, which was then expressed as nonnalized particle concentration contours using computer programs developed for this study. / The study quantitatively revealed the distinctive patient exhaled airflow patterns and the extent of bioaerosol, generated directly from the patient source with the application of different oxygen delivery interventions for different patient lung conditions and oxygen flow rates. It was found that contamination was more critical during the administration of oxygen therapies, which is common in clinical circumstances. Source control is therefore the most efficient and effective approach to the reduction and even elimination of patient exhaled bioaerosol contaminants. Thus, when working in an isolation room environment, full preventive measure should be taken and it is essential to consider the location of mechanical vents and the patient exhaled airflow patterns. It has also been shown in experiment that applications of bacterial viral filter could be a solution to the problem. / Chow, Ka Ming. / Advisers: Puay Peng Ho; Jin Yeu Tsou. / Source: Dissertation Abstracts International, Volume: 73-09(E), Section: A. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 115-147). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.
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