[Show abstract][Hide abstract] ABSTRACT: Indoor transmission of respiratory droplets bearing influenza within humans poses high risks to respiratory function deterioration and death. Therefore, we aimed to develop a framework for quantifying the influenza infection risk based on the relationships between inhaled/exhaled respiratory droplets and airborne transmission dynamics in a ventilated airspace. An experiment was conducted to measure the size distribution of influenza-containing droplets produced by coughing for a better understanding of potential influenza spread. Here we integrated influenza population transmission dynamics, a human respiratory tract model, and a control measure approach to examine the indoor environment–virus–host interactions. A probabilistic risk model was implemented to assess size-specific infection risk for potentially transmissible influenza droplets indoors. Our results found that there was a 50% probability of the basic reproduction number (
) exceeding 1 for small-size influenza droplets of 0·3–0·4
m, implicating a potentially high indoor infection risk to humans. However, a combination of public health interventions with enhanced ventilation could substantially contain indoor influenza infection. Moreover, the present dynamic simulation and control measure assessment provide insights into why indoor transmissible influenza droplet-induced infection is occurring not only in upper lung regions but also in the lower respiratory tract, not normally considered at infection risk.
Epidemiology and Infection 07/2015; -1:1-13. DOI:10.1017/S0950268815001739 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: SUMMARY Dengue, one of the most important mosquito-borne diseases, is a major international public health concern. This study aimed to assess potential dengue infection risk from Aedes aegypti in Kaohsiung and the implications for vector control. Here we investigated the impact of dengue transmission on human infection risk using a well-established dengue-mosquito-human transmission dynamics model. A basic reproduction number (R 0)-based probabilistic risk model was also developed to estimate dengue infection risk. Our findings confirm that the effect of biting rate plays a crucial role in shaping R 0 estimates. We demonstrated that there was 50% risk probability for increased dengue incidence rates exceeding 0·5-0·8 wk-1 for temperatures ranging from 26°C to 32°C. We further demonstrated that the weekly increased dengue incidence rate can be decreased to zero if vector control efficiencies reach 30-80% at temperatures of 19-32°C. We conclude that our analysis on dengue infection risk and control implications in Kaohsiung provide crucial information for policy-making on disease control.
Epidemiology and Infection 07/2014; 143(05):1-14. DOI:10.1017/S0950268814001745 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: SUMMARY Influenza poses a significant public health burden worldwide. Understanding how and to what extent people would change their behaviour in response to influenza outbreaks is critical for formulating public health policies. We incorporated the information-theoretic framework into a behaviour-influenza (BI) transmission dynamics system in order to understand the effects of individual behavioural change on influenza epidemics. We showed that information transmission of risk perception played a crucial role in the spread of health-seeking behaviour throughout influenza epidemics. Here a network BI model provides a new approach for understanding the risk perception spread and human behavioural change during disease outbreaks. Our study allows simultaneous consideration of epidemiological, psychological, and social factors as predictors of individual perception rates in behaviour-disease transmission systems. We suggest that a monitoring system with precise information on risk perception should be constructed to effectively promote health behaviours in preparation for emerging disease outbreaks.
Epidemiology and Infection 03/2014; 143(01):1-14. DOI:10.1017/S0950268814000430 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: SUMMARY Understanding how seasonality shapes the dynamics of tuberculosis (TB) is essential in determining risks of transmission and drug resistance in (sub)tropical regions. We developed a relative fitness-based multidrug-resistant (MDR) TB model incorporated with seasonality and a probabilistic assessment model to assess infection risk in Taiwan regions. The model accurately captures the seasonal transmission and population dynamics of TB incidence during 2006-2008 and MDR TB in high TB burden areas during 2006-2010 in Taiwan. There is ∼3% probability of having exceeded 50% of the population infected attributed to MDR TB. Our model not only provides insight into the understanding of the interactions between seasonal dynamics of TB and environmental factors but is also capable of predicting the seasonal patterns of TB incidence associated with MDR TB infection risk. A better understanding of the mechanisms of TB seasonality will be critical in predicting the impact of public control programmes.
Epidemiology and Infection 05/2013; 142(02):1-13. DOI:10.1017/S0950268813001040 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: SUMMARY We investigated the cost-effectiveness of different influenza control strategies in a school setting in Taiwan. A susceptible-exposure-infected-recovery (SEIR) model was used to simulate influenza transmission and we used a basic reproduction number (R 0)-asymptomatic proportion (θ) control scheme to develop a cost-effectiveness model. Based on our dynamic transmission model and economic evaluation, this study indicated that the optimal cost-effective strategy for all modelling scenarios was a combination of natural ventilation and respiratory masking. The estimated costs were US$10/year per person in winter for one kindergarten student. The cost for hand washing was estimated to be US$32/year per person, which was much lower than that of isolation (US$55/year per person) and vaccination (US$86/year per person) in containing seasonal influenza. Transmission model-based, cost-effectiveness analysis can be a useful tool for providing insight into the impacts of economic factors and health benefits on certain strategies for controlling seasonal influenza.
Epidemiology and Infection 03/2013; 141(12):1-14. DOI:10.1017/S0950268813000423 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to link Fick's type mass transfer and biokinetics together with Michaelis-Menten kinetics to arrive at a simple predictive framework for quantifying biouptake mechanisms in gills of freshwater clam Corbicula fluminea exposed to Cu(II). A diffusion-based Cu(II) influx and permeability can be calculated using physiological and allometric-related parameters. Simulations indicate that Cu(II) bioconcentration factor of gills was 42. Estimated steady-state Cu(II) gill uptake influx and permeability were 0.097 nmol cm(-2) s(-1) and 0.48 cm s(-1), respectively. The proposed simple allometric diffusion-based biokinetic model meets the need for describing nonequilibrium aspects of biouptake mechanisms in bivalve gills.
Bulletin of Environmental Contamination and Toxicology 06/2010; 84(6):703-7. DOI:10.1007/s00128-010-0011-3 · 1.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study aimed to estimate the natural history and transmission parameters based on experimental viral shedding and symptom dynamics in order to understand the key epidemiological factors that characterize influenza (sub)type epidemics. A simple statistical algorithm was developed by combining a well-defined mathematical scheme of epidemiological determinants and experimental human influenza infection. Here we showed that (i) the observed viral shedding dynamics mapped successfully the estimated time-profile of infectiousness and (ii) the profile of asymptomatic probability was obtained based on observed temporal variation of symptom scores. Our derived estimates permitted evaluation of relationships between various model-derived and data-based estimations, allowing evaluation of trends proposed previously but not tested fully. As well as providing insights into the dynamics of viral shedding and symptom scores, a more profound understanding of influenza epidemiological parameters and determinants could enhance the viral kinetic studies of influenza during infection in the respiratory tracts of experimentally infected individuals.
Epidemiology and Infection 11/2009; 138(6):825-35. DOI:10.1017/S0950268809991178 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to develop a biologically based risk assessment model for human health through consumption of arsenic (As) contaminated farmed tilapia (Oreochromis mossambicus) from blackfoot disease (BFD)-endemic area in Taiwan for estimating the consumption advice. We linked a physiologically based pharmacokinetic (PBPK) and a pharmacodynamic (PD) model to account for the exposure and dose-response profiles of As in human. Risk analysis indicates that consumption of farmed tilapia poses no significant threat from As-induced lung and bladder cancers. The predicted risk-based median consumption advice was no more than 5-17 meals month(-1) (or 2-6 g day(-1)).
Bulletin of Environmental Contamination and Toxicology 06/2009; 83(1):108-14. DOI:10.1007/s00128-009-9764-y · 1.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We coupled the Wells-Riley equation and the susceptible-exposed-infected-recovery (SEIR) model to quantify the impact of the combination of indoor air-based control measures of enhanced ventilation and respiratory masking in containing pandemic influenza within an elementary school. We integrated indoor environmental factors of a real elementary school and aetiological characteristics of influenza to estimate the age-specific risk of infection (P) and basic reproduction number (R(0)). We combined the enhanced ventilation rates of 0.5, 1, 1.5, and 2/h and respiratory masking with 60%, 70%, 80%, and 95% efficacies, respectively, to predict the reducing level of R0. We also took into account the critical vaccination coverage rate among schoolchildren. Age-specific P and R(0) were estimated respectively to be 0.29 and 16.90; 0.56 and 16.11; 0.59 and 12.88; 0.64 and 16.09; and 0.07 and 2.80 for five age groups 4-6, 7-8, 9-10, 11-12, and 25-45 years, indicating pre-schoolchildren have the highest transmission potential. We conclude that our integrated approach, employing the mechanism of transmission of indoor respiratory infection, population-dynamic transmission model, and the impact of infectious control programmes, is a powerful tool for risk profiling prediction of pandemic influenza among schoolchildren.
Epidemiology and Infection 09/2008; 136(8):1035-45. DOI:10.1017/S0950268807009284 · 2.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the present study, a stage-classified exposure model is developed to better characterize long-term arsenic (As) accumulation of both genders of children, adolescents, and adults through tilapia consumption in Taiwan. Ingestion rate as well as elimination rate of As are treated dynamically and are used to parameterize the stage-classified accumulation model. Model simulations are carried out to produce temporal changes of As body burden of the residents who consume tilapia from blackfoot disease (BFD)-endemic area in three major cities in Taiwan. The model presented here can be served as a strong framework for refining human health risk assessments through fish consumption.
Bulletin of Environmental Contamination and Toxicology 04/2008; 80(3):289-93. DOI:10.1007/s00128-008-9365-1 · 1.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract
Abstract Recently developed control measure modeling approaches for containing airborne infections, including engineering controls with respiratory protection and public health interventions, are readily amenable to an integrated-scale analysis. Here we show that such models can be derived from an integrated-scale analysis generated from three different types of functional relationship: Wells–Riley mathematical model, competing-risks model, and Von Foerster equation, both of the key epidemiological determinants involved and of the functional connections between them. We examine mathematically the impact of engineering control measures such as enhanced air exchange and air filtration rates with personal masking combined with public health interventions such as vaccination, isolation, and contact tracing in containing the spread of indoor airborne infections including influenza, chickenpox, measles, and severe acute respiratory syndrome (SARS). If enhanced engineering controls could reduce the basic reproductive number (R0) below 1.60 for chickenpox and 3 for measles, our simulations show that in such a prepared response with public health interventions would have a high probability of containing the indoor airborne infections. Combinations of engineering control measures and public health interventions could moderately contain influenza strains with an R0 as high as 4. Our analysis indicates that effective isolation of symptomatic patients with low-efficacy contact tracing is sufficient to control a SARS outbreak. We suggest that a valuable added dimension to public health inventions could be provided by systematically quantifying transmissibility and proportion of asymptomatic infection of indoor airborne infection.
Indoor Air 01/2007; 16(6):469-81. DOI:10.1111/j.1600-0668.2006.00443.x · 4.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a bioenergetics-based approach to analyze the chronic effects and growth toxicity mode of action in tilapia Oreochromis mossambicus exposed to waterborne As and to predict fish growth under different exposure scenarios. 7-day exposure bioassays showed that tilapia accumulate As when exposed to waterborne As. We conducted growth bioassays to assess chronic As toxicity to tilapia. We incorporated a universal ontogenetic growth model with the DEB(tox )theory to explore the mode of action of As toxicity. Our results show that the specific growth rates of exposed tilapia are inversely proportional to As concentrations and are calculated as 0.76% d(-1) in 0 microg mL(-1), 0.57% d(-1) in 1 microg mL(-1), 0.2 % d(-1) in 2 microg mL(-1), and 0.04% d(-1) in 4 microg mL(-1) As, respectively. We showed that the internal threshold concentration did not change significantly with time, demonstrating that the critical body residue approach is applicable for As toxicity assessment. We distinguished between three modes of action of As, including direct effects on growth and indirect effects by way of maintenance and food consumption. Our results support that decreased feeding accounts for the growth decrease in the case of feeding ad libitum. The feeding decrease model also illustrates the growth trajectories of tilapia during the entire whole life span, suggesting that the maximum biomass of tilapia are 1038.75 g in uncontaminated water and 872.97 g in 1 microg mL(-1), 403.06 g in 2 microg mL(-1), and 336.65 g in 4 microg mL(-1) As, respectively. We suggest that considering modes of action in ecotoxicology not only improves our understanding of the toxicities of chemicals, it is also useful in setting up models and avoiding pitfalls in species- and site-specific environmental risk assessment. This proposed framework for tilapia gives preliminary information relevant to aquacultural and ecologic management.
Archives of Environmental Contamination and Toxicology 02/2006; 50(1):144-52. DOI:10.1007/s00244-005-1054-z · 1.90 Impact Factor