Rethinking ventilation design for reducing airborne respiratory disease transmission in general hospital wards
Student thesis: Doctoral Thesis
The widespread 2003 outbreak of SARS that claimed so many lives in Hong Kong was said to be due to hidden carriers responsible for spread of the disease to the community from public hospitals. SARS-infected patients with not yet recognizable and appreciable symptoms, so-called hidden spreaders, having been housed in general wards of hospitals, transmitted the disease unnoticeably. Precautions were subsequently taken because of the known likelihood of airborne transmission of SARS. However, at that time, isolation rooms that were set up in hospitals in regions and countries being attacked by SARS, such as Hong Kong, Singapore and Taiwan, were very much overwhelmed by the massive influx of patients with probable or suspected SARS. To accommodate the situation, some temporary makeshift ventilation modifications were identified and swiftly incorporated into general hospital wards to tackle the surge in patients. Indeed, this project study touched on the two key problem areas arising from the most recent SARS outbreak. These two industry problems have not yet received the necessary attention not to mention any resolution, and the study here is applying existing engineering knowledge in succinct and rigorous way to solve them with views to protect hospital occupants from airborne infectious disease attack. The first problem is on "how to improve the isolation capability of existing general hospital wards to reduce the chance of cross infection due to hidden spreader". The second problem is on "how to make available a fast track sufficient quantity of isolation beds to meet patient surge in an infectious disease outbreak". In addressing these two problems, this study focuses on identifying effective engineering control measures on indoor ventilation system design to minimize the spread of airborne respiratory diseases. The study adopts the proven methodology of computational fluid dynamics (CFD) analysis to simulate and compare the removal of microbes in a number of different hypothetical ventilation setups. The CFD approach was used to eliminate the risks of exposure to infectious pathogens that would occur in a real-life study. In tackling the first question, the first objective of the thesis is to use CFD to verify a simple and cost-effective ventilation setup in a general ward by enhancing the ventilation air flow path and boosting up the air flow rate. This setting new was shown to match the CDC’s isolation facilities standard to restrict the spread of airborne infectious diseases in hospitals. This was a long-term solution for hospitals to upgrade their general ward ventilation systems. With these improvements, it is possible to match the standards maintained in a properly constructed isolation room but at a much lower cost. It is recommended that the newly identified ventilation parameters be widely adopted in the design of new general hospital wards to minimize cross-infection. Existing general hospital wards can be retrofitted at far less disruption and cost than would be incurred by full-scale refurbishment. The second objective o this thesis is to use CFD to verify the fast-track, makeshift isolation setup of window mounted extract fans being incorporated during the 2003 SARS outbreak. It is a short-term, emergency approach and is recommended for hospitals to deal with patient surges in case of an airborne disease pandemic. When there is a shortage of isolation facilities to accommodate a pandemic surge in patients, the proposed ventilation setup should be added to existing general wards to minimize cross-infection, and these fans can simply be taken down after the surge. In view of the great possibility of the emergence of new infectious diseases and of the ever increasing popularity of cross-country travel, the study of the ventilation setup in general hospital wards should not remain in its current state. These studies will help stopping the nosocomial transmission of infectious diseases by hidden spreaders at the verge of a disease outbreak, and also contain the massive isolation patient surge in case there is an outbreak.
- Hospital buildings, Design and construction, Airborne infection, Prevention, Hospital wards, Heating and ventilation