Study on Emission and Dispersion of Contaminated Aerosols from Toilet Flushing with Implications for Pathogen Transmission and the Effectiveness of Disinfection by UV-C

Description

After the 2003 outbreak of severe acute respiratory syndrome (SARS), people in Hong Kong began paying more attention to the hygiene of toilets. Although we have known for some time about potential human exposure to flushing-associated water droplets in toilets, very little is known about the aerosolization and deposition of flushing-associated pathogens and their implications for public health, particularly in areas with poorly designed toilet systems or high frequency use public toilets, such as those in Hong Kong. Solid waste from individuals suffering intestinal or urinary colonization by pathogenic microorganisms may contain a huge number of bacteria or viruses. Washroom users can be infected by either primary exposure, through the inhalation of contaminated aerosols, or secondary exposure, through contact with contaminated surfaces.There has been very little systematic research on minimizing exposure risks. Preliminary results show that ultraviolet light of 254 nm wavelength (UV-C) has disinfection capabilities in indoor environments, although no study to date has considered on the role of toilets in possible spreading of infection.Given that the existing body of knowledge is far from complete relative to the potential importance of the topic, our proposed work aims to bridge the knowledge gaps in our understanding of pathogen exposure during toilet flushing and suitable mitigating measures.The focus will be on investigating the effects of such toilet system parameters as bowl design, flushing mechanisms, water flow rate, and water pressure, such physical parameters as feces consistency, and such environmental factors as the ventilation system on the emission of and exposure to contaminated aerosols. Another key aim is to examine the disinfection effectiveness of UV-C sources, i.e., upper-room ultraviolet germicidal irradiation (UVGI) and localized UV-C developed by the PI.Both experimental and numerical approaches will be adopted. A custom-built toilet system will be installed in a controlled chamber, and common intestinal pathogens will be tested. The emission factors for the modeled feces will be measured for the first time. Field measurements will be carried out in real toilets. Airborne and surface samples will be collected under various testing scenarios and controlled conditions.Based on the measured emission characteristics, a numerical tool will be developed to predict the transport of pathogens and disinfection effectiveness. The effectiveness of UV-C devices will also be tested in real toilets. The output of this work will be applicable in a wide range of contexts, including exposure risk control and the optimization of UV-C installations.