Joseph Kai Cho Kwan

A methodology for estimating airborne virus exposures in indoor environments using the spatial distribution of expiratory aerosols and virus viability characteristics

UNLABELLED This study investigated the feasibility of using the spatial distribution of expiratory aerosols and the viability functions of airborne viruses to estimate exposures to airborne viruses in an indoor environment under imperfectly mixed condition. A method adopting this approach was tested in an air-conditioned hospital ward. Artificial coughs were produced by aerosolizing a simulated respiratory fluid containing a known concentration of benign bacteriophage. The bacteriophage exposures estimated on the basis of the spatial aerosol distributions and its viability function were in reasonable agreement with those measured directly by biological air sampling and culturing. The ventilation flow and coughing orientation were found to play significant roles in aerosol transport, leading to different spatial distribution patterns in bacteriophage exposure. Bacteriophage exposures decreased with lateral distance from the infector when the infector coughed vertically upward. In contrast, exposures were constant or even increased with distance in the case of lateral coughing. The possibility of incorporating the proposed exposure estimation into a dose-response model for infection risk assessment was discussed. The study has also demonstrated the potential application of viability functions of airborne viral pathogens in exposure assessment and infection risk analysis, which are often unavailable in literature for some important communicable diseases. PRACTICAL IMPLICATIONS The proposed method makes use of the viability function of the virus and the spatial distribution of the expiratory aerosols for virus exposure estimation. Spatial differences in aerosol distribution and its influences on virus exposure in an air space can be determined. Variations in infectious dose with carrier aerosol size could also be considered. The proposed method may serve as a tool for further investigation of ventilation design and infection control in clinical or other indoor environments.

Application of vitamin E to antagonize SWCNTs-induced exacerbation of allergic asthma

The aggravating effects of zero-dimensional, particle-shaped nanomaterials on allergic asthma have been previously investigated, but similar possible effects of one-dimensional shaped nanomaterials have not been reported. More importantly, there are no available means to counteract the adverse nanomaterial effects to allow for their safe use. In this study, an ovalbumin (OVA)-sensitized rat asthma model was established to investigate whether single walled carbon nanotubes (SWCNTs) aggravate allergic asthma. The results showed that SWCNTs in rats exacerbated OVA-induced allergic asthma and that this exacerbation was counteracted by concurrent administration vitamin E. A mechanism involving the elimination of reactive oxygen species, downregulation of Th2 responses, reduced Ig production, and the relief of allergic asthma symptoms was proposed to explain the antagonistic effects of vitamin E. This work could provide a universal strategy to effectively protect people with allergic asthma from SWCNTs or similar nanomaterial-induced aggravating effects.

An evaluation of the ventilation performance of new SARS isolation wards in nine hospitals in Hong Kong

In response to the 2003 outbreak of severe acute respiratory syndrome (SARS) the Hong Kong Government promptly constructed 558 new state-of-the-art SARS isolation rooms with more than 1300 beds in 14 hospitals. These were completed by the end of 2003 and some will be available for H5N1 influenza patients, if any human cases occur. We investigated the ventilation of the wards after 18 months of operation and identified the major factors that affect ventilation effectiveness. Negative pressure, airflow path, air change rate and local ventilation effectiveness in selected rooms in 9 major hospitals were measured and their performance assessed against CDC requirements. Testing in 38 rooms found that 97% met the recommended negative pressure difference of 2.5 Pa between corridor and anteroom, 89% of 48 met the same requirement between anteroom and cubicle. No leakage of air to the corridor was found, but 60% of the toilets/bathrooms were operated under positive pressure. Over 90% of corridor-anteroom or anteroom-cubicle doors had bi-directional flow when the door was open. Of 35 tested cubicles, 26% had an air change rate <12 ACH and their ventilation was non-uniform. Despite using state-of-the-art technologies, 28% of the rooms tested still failed to meet the 12 ACH ventilation requirement and 60% had the wrong airflow direction for the toilets/bathrooms, but all satisfied the requirement of no air leakage to the corridor. Regular checks of airflow direction and air change rate are highly recommended together with specific education or training of hospital maintenance engineers and health care workers.

The Use of Nonlinear Acoustics as an Energy-Efficient Technique for Aerosol Removal

This article is a feasibility study on using nonlinear acoustic effects, acoustic streaming and acoustic radiation pressure, for aerosol removal in an air duct. Unlike previous research, which used acoustics solely to cause aerosol agglomeration prior to aerosol removal in traditional duct collection systems, this article considers the acoustic streaming effect, which is significant but was previously neglected. Monodispersed polystyrene spheres with diameters ranging from 0.3 to 6 μm were tested. The proposed system removed 12–20% of the submicron aerosols and 25–32% of the micron aerosols when the airflow rate was approximately 90 L/min. Acoustic streaming introduces stagnation points on the surface of the air duct and removes the aerosols by deposition. Acoustic radiation pressure causes aerosols to form agglomerates. This enhances inertial impaction and/or gravitational sedimentation, which further enhances the removal efficiency of micron aerosols. The particle-removal efficiency is proportional to the duration that the aerosols are exposed to the acoustic field. The pressure drop due to the nonlinear acoustic effects is negligible; thus, power consumption is minimal. This system has the potential to be developed into an energy-efficient technique for aerosol removal. Copyright 2014 American Association for Aerosol Research

Effects of Surface Material, Ventilation, and Human Behavior on Indirect Contact Transmission Risk of Respiratory Infection

Infectious particles can be deposited on surfaces. Susceptible persons who contacted these contaminated surfaces may transfer the pathogens to their mucous membranes via hands, leading to a risk of respiratory infection. The exposure and infection risk contributed by this transmission route depend on indoor surface material, ventilation, and human behavior. In this study, quantitative infection risk assessments were used to compare the significances of these factors. The risks of three pathogens, influenza A virus, respiratory syncytial virus (RSV), and rhinovirus, in an aircraft cabin and in a hospital ward were assessed. Results showed that reducing the contact rate is relatively more effective than increasing the ventilation rate to lower the infection risk. Nonfabric surface materials were found to be much more favorable in the indirect contact transmission for RSV and rhinovirus than fabric surface materials. In the cases considered in this study, halving the ventilation rate and doubling the hand contact rate to surfaces and the hand contact rate to mucous membranes would increase the risk by 3.7–16.2%, 34.4–94.2%, and 24.1–117.7%, respectively. Contacting contaminated nonfabric surfaces may pose an indirect contact risk up to three orders of magnitude higher than that of contacting contaminated fabric surfaces. These findings provide more consideration for infection control and building environmental design.

Studies on detachment behavior of micron sized droplets: A comparison between pure fluid and nanofluid

ABSTRACT Resuspension is considered as a source of indoor air pollutants. These airborne pollutants can be in the form of liquid or solid. It has been previously found that the detachment mechanism of liquid droplets is different from the solid particles on the poly(methyl methacrylate) (PMMA) surface. Liquid droplets detach by portion when they are under an increasing normal force field while droplets detach completely when under a tangential force field. In this research, droplet detachment experiments are extended to different substrate materials, which are PMMA, glass, and stainless steel by the means of centrifuge. Also, the differences in detachment between pure glycerol-water (pure fluid) and a glycerol solution with the addition of nanoparticles (nanofluid) are investigated under different substrate materials. It is found that liquid droplets, again, detach by portion under normal force for all the substrate materials. For tangential force, the droplets detach completely if the exerted force was sufficiently large and the threshold values are material dependent, which is further elaborated by retention theory. After the addition of nanoparticles, a higher removal force was required compared to the droplets of pure fluid within the same size range. Also, solid residues with a negligible amount of fluid were found on the substrate after each removal of droplets under both normal and tangential force. The involvement of nanoparticles could be the pioneer work for future studies on commonly found liquid pollutants, which are prone to be contaminated by solid particles, such as in salivary excretion. Copyright

A Respiratory Tract Infection Index for SARS and Avian Influenza Outbreaks

A respiratory tract infection index (RTII) was developed to predict potential outbreaks of infectious respiratory diseases in the community. The index incorporates a variety of meteorological conditions and air pollution factors. In the first phase of our study, we reviewed the index values around certain typical epidemiological events by retrospective calculation. The results showed that significantly high index values were recorded right before the occurrences of the events. This finding suggests that the RTII index appears to be a good indicator for public health officials and the public for taking early preventative measures against infectious respiratory diseases such as SARS and avian influenza. Further statistical analyses will be conducted in the second phase of the study to validate the efficiency and generality of the index