Jianjian Wei

Numerical investigation of wind-driven natural ventilation performance in a multi-storey hospital by coupling indoor and outdoor airflow:

This study employed two ventilation indexes: local mean age of air and air change rate per hour, to investigate wind-induced natural ventilation of 260 wards of a multi-storey hospital building in suburb of Guangzhou using computational fluid dynamics simulations. Using the surface-grid extrusion technique, high-quality hexahedral grid cells were generated for the coupled outdoor and indoor airflow field. Turbulence was solved by the renormalisation group k-ɛ model validated against experimental data with grid independence studies. Homogeneous tracer gas emission was adopted to predict room age of air. The air change rate of cross ventilation and single-sided ventilation can reach 30–160 h−1 and 0.5–7 h−1, respectively. Due to different locations of room openings on the balconies, natural ventilation of a room can be greatly better than its neighbouring room. The wind-induced cross ventilation highly depends on the distance from the room opening to the stagnation point and on the resulting pressure distribution on the target building surface. Furthermore, it is significantly influenced by the upstream buildings, the bent shape of the target building, and the prevailing wind directions. The coupled computational fluid dynamics methodologies with integrated ventilation indexes are useful for assessing the natural ventilation performance in other complex built environments.

A study of the probable transmission routes of MERS‐CoV during the first hospital outbreak in the Republic of Korea

Abstract Infections caused by the Middle East respiratory syndrome coronavirus (MERS‐CoV) are a serious health issue due to their prevalence and associated mortality. However, the transmission routes of the virus remain unclear, and thus, the current recommended control strategies are not evidence based. In this study, we investigated the transmission routes of MERS‐CoV during the first nosocomial outbreak in the Republic of Korea in May 2015 using a multi‐agent modeling framework. We identified seven hypothesized transmission modes based on the three main transmission routes (long‐range airborne, close contact, and fomite). The infection risks for each hypothesis were estimated using the multi‐agent modeling framework. Least‐squares fitting was conducted to compare the distribution of the predicted infection risk in the various scenarios with that of the reported attack rates and to identify the hypotheses with the best fit. In the scenarios in which the index patient was a super‐spreader, our model simulations suggested that MERS‐CoV probably spread via the long‐range airborne route. However, it is possible that the index patient shed an average viral load comparable to the loads reported in the literature, and that transmission occurred via a combined long‐range airborne and close contact route.

Assessing the risk of downwind spread of avian influenza virus via airborne particles from an urban wholesale poultry market

Interspecies transmissions of avian influenza viruses (AIV) occur at the human-poultry interface, among which the live poultry markets (LPMs) are easily assessed by urban residents. Thousands of live poultry from different farms arrive daily at wholesale markets before being sold to retail markets. We assessed the risk of AIV downwind spread via airborne particles from a representative wholesale market in Guangzhou. Air samples were collected using the cyclone-based NIOSH bioaerosol samplers at different locations inside a wholesale market, and viral RNA and avian 18S RNA were quantified using quantitative real-time RT-PCR. Computational Fluid Dynamics (CFD) modeling was performed to investigate the AIV spread pattern. Viral RNA was readily detected from 19 out of 21 air sampling events, predominantly from particles larger than 1 µm. The concentration of viral RNA detected at the poultry holding area was 4.4 × 105 copies/m3 and was as high as 2.6 × 104 copies/m3 100 m downwind. A high concentration of avian 18S RNA (2.5 × 108 copies/m3) detected at the poultry holding area was used for assessing the potential spread of avian influenza virus during outbreak situations. CFD modeling indicated the combined effect of wind direction and surrounding buildings on the spread of virus and a slow decay rate of the virus in the air in the downwind direction. Because of the large volume of poultry trade daily, wholesale markets located in urban areas may pose considerable AIV infection risk to neighboring residents via wind spread, even in the absence of direct contact with poultry.

Numerical modeling of particle deposition in ferret airways: A comparison with humans

ABSTRACT The ferret is commonly used as an animal model for studying human respiratory diseases, but the validation is lacking. The particle deposition patterns in ferret airways was investigated and compared to those in humans. A computational fluid dynamics method was used to simulate particle deposition in the tracheobronchial airway by using the truncated single-path models. The deposition characteristics of particles with diameters of 1, 3, and 5 μm were investigated under various respiratory rates at different activity conditions (i.e., sedentary, light, moderate, and intense activities). For both human and ferret models, deposition increased with both generation and particle size but decreased with respiratory rate. Particles of 1–5 μm deposit more but transport upper in ferrets than in humans, which suggests that ferrets are more likely to be infected in the proximal airways. The results show that the trend of particle deposition in the ferret airways is similar to that in human airways but with different deposition rates and sites. Our findings indicate that ferret for studying human respiratory diseases is suitable for the upper respiratory diseases, such as human influenza, but may not be suitable for studying the lower respiratory diseases, such as pneumonia. Copyright

Potential impact of a ventilation intervention for influenza in the context of a dense indoor contact network in Hong Kong.

Emerging diseases may spread rapidly through dense and large urban contact networks. We constructed a simple but novel dual-contact network model to account for both airborne contact and close contact of individuals in the densely populated city of Hong Kong. The model was then integrated with an existing epidemiological susceptible-exposed-infectious-recovered (SEIR) model, and we used a revised Wells-Riley model to estimate infection risks by the airborne route and an exponential dose-response model for risks by the contact and droplet routes. A potential outbreak of partially airborne influenza was examined, assuming different proportions of transmission through the airborne route. Our results show that building ventilation can have significant effects in airborne transmission-dominated conditions. Moreover, even when the airborne route only contributes 20% to the total infection risk, increasing the ventilation rate has a strong influence on transmission dynamics, and it also can achieve control effects similar to those of wearing masks for patients, isolation and vaccination.

Building Ventilation as an Effective Disease Intervention Strategy in a Dense Indoor Contact Network in an Ideal City.

Emerging diseases may spread rapidly through dense and large urban contact networks, especially they are transmitted by the airborne route, before new vaccines can be made available. Airborne diseases may spread rapidly as people visit different indoor environments and are in frequent contact with others. We constructed a simple indoor contact model for an ideal city with 7 million people and 3 million indoor spaces, and estimated the probability and duration of contact between any two individuals during one day. To do this, we used data from actual censuses, social behavior surveys, building surveys, and ventilation measurements in Hong Kong to define eight population groups and seven indoor location groups. Our indoor contact model was integrated with an existing epidemiological Susceptible, Exposed, Infectious, and Recovered (SEIR) model to estimate disease spread and with the Wells-Riley equation to calculate local infection risks, resulting in an integrated indoor transmission network model. This model was used to estimate the probability of an infected individual infecting others in the city and to study the disease transmission dynamics. We predicted the infection probability of each sub-population under different ventilation systems in each location type in the case of a hypothetical airborne disease outbreak, which is assumed to have the same natural history and infectiousness as smallpox. We compared the effectiveness of controlling ventilation in each location type with other intervention strategies. We conclude that increasing building ventilation rates using methods such as natural ventilation in classrooms, offices, and homes is a relatively effective strategy for airborne diseases in a large city.

Defining the sizes of airborne particles that mediate influenza transmission in ferrets

Significance Emerging respiratory pathogens pose significant public health threats as a result of their potential for rapid global spread via multiple non-mutually exclusive modes of transmission. The relative significance of contact, droplet, and airborne transmission for many respiratory pathogens remains a knowledge gap, and better understanding is essential for developing evidence-based measures for effective infection control. Here, we describe and evaluate a transmission chamber that separates virus-laden particles in air by size to study airborne particles that mediate influenza transmission in ferrets. Our results provide direct experimental evidence of influenza transmission via droplets and fine droplet nuclei, albeit at different efficiency. This transmission device can also be applied to elucidate the mode of transmission of other respiratory pathogens. Epidemics and pandemics of influenza are characterized by rapid global spread mediated by non-mutually exclusive transmission modes. The relative significance between contact, droplet, and airborne transmission is yet to be defined, a knowledge gap for implementing evidence-based infection control measures. We devised a transmission chamber that separates virus-laden particles by size and determined the particle sizes mediating transmission of influenza among ferrets through the air. Ferret-to-ferret transmission was mediated by airborne particles larger than 1.5 µm, consistent with the quantity and size of virus-laden particles released by the donors. Onward transmission by donors was most efficient before fever onset and may continue for 5 days after inoculation. Multiple virus gene segments enhanced the transmissibility of a swine influenza virus among ferrets by increasing the release of virus-laden particles into the air. We provide direct experimental evidence of influenza transmission via droplets and fine droplet nuclei, albeit at different efficiency.

Low re-inhalation of the exhaled flow during normal nasal breathing in a pediatric airway replica

Abstract To estimate the fraction of the exhaled airflow that is re-inhaled during normal nasal breathing, experiments were carried out in a water tank with an anatomically accurate respiratory tract model of a 4-year-old child. The velocity of respiratory flow was scaled using similarity laws between air and water. Breath simulation was performed via a computer-controlled piston-cylinder system. Food-dye visualization allows a qualitative analysis of the re-inhaled fraction of this exhaled flow. For the quantitative analysis, neutrally buoyant particles were added to the water medium, and illuminated by the laser which illuminates the whole breathing region of the respiratory model, such that the trajectory and quantity of the re-inhaled particles can be recorded and counted. The experimental results in the pediatric airway replica show that a negligible fraction (<0.06%) of the exhaled airflow is re-inhaled during normal nasal breathing in the absence of the rising thermal plume. The artificial plume generated by a heated aluminium brick at the tank bottom increases the re-inhalation ratio by 4 times under the investigated case (albeit still at a very low value of 0.15%). Our results thus reveal that during normal nasal breathing in the present pediatric subject, the vast majority of human exhaled airflow escapes from the inhalation zone and is not re-inhaled.