43 research outputs found
The effect of travel restrictions on the spread of a moderately contagious disease
BACKGROUND: Much research in epidemiology has been focused on evaluating conventional methods of control strategies in the event of an epidemic or pandemic. Travel restrictions are often suggested as an efficient way to reduce the spread of a contagious disease that threatens public health, but few papers have studied in depth the effects of travel restrictions. In this study, we investigated what effect different levels of travel restrictions might have on the speed and geographical spread of an outbreak of a disease similar to severe acute respiratory syndrome (SARS). METHODS: We used a stochastic simulation model incorporating survey data of travel patterns between municipalities in Sweden collected over 3 years. We tested scenarios of travel restrictions in which travel over distances >50 km and 20 km would be banned, taking into account different levels of compliance. RESULTS: We found that a ban on journeys >50 km would drastically reduce the speed and geographical spread of outbreaks, even when compliance is < 100%. The result was found to be robust for different rates of intermunicipality transmission intensities. CONCLUSION: This study supports travel restrictions as an effective way to mitigate the effect of a future disease outbreak
Modeling influenza epidemics and pandemics: insights into the future of swine flu (H1N1)
Here we present a review of the literature of influenza modeling studies, and discuss how these models can provide insights into the future of the currently circulating novel strain of influenza A (H1N1), formerly known as swine flu. We discuss how the feasibility of controlling an epidemic critically depends on the value of the Basic Reproduction Number (R0). The R0 for novel influenza A (H1N1) has recently been estimated to be between 1.4 and 1.6. This value is below values of R0 estimated for the 1918–1919 pandemic strain (mean R0~2: range 1.4 to 2.8) and is comparable to R0 values estimated for seasonal strains of influenza (mean R0 1.3: range 0.9 to 2.1). By reviewing results from previous modeling studies we conclude it is theoretically possible that a pandemic of H1N1 could be contained. However it may not be feasible, even in resource-rich countries, to achieve the necessary levels of vaccination and treatment for control. As a recent modeling study has shown, a global cooperative strategy will be essential in order to control a pandemic. This strategy will require resource-rich countries to share their vaccines and antivirals with resource-constrained and resource-poor countries. We conclude our review by discussing the necessity of developing new biologically complex models. We suggest that these models should simultaneously track the transmission dynamics of multiple strains of influenza in bird, pig and human populations. Such models could be critical for identifying effective new interventions, and informing pandemic preparedness planning. Finally, we show that by modeling cross-species transmission it may be possible to predict the emergence of pandemic strains of influenza
Phase transitions in contagion processes mediated by recurrent mobility patterns
Human mobility and activity patterns mediate contagion on many levels,
including the spatial spread of infectious diseases, diffusion of rumors, and
emergence of consensus. These patterns however are often dominated by specific
locations and recurrent flows and poorly modeled by the random diffusive
dynamics generally used to study them. Here we develop a theoretical framework
to analyze contagion within a network of locations where individuals recall
their geographic origins. We find a phase transition between a regime in which
the contagion affects a large fraction of the system and one in which only a
small fraction is affected. This transition cannot be uncovered by continuous
deterministic models due to the stochastic features of the contagion process
and defines an invasion threshold that depends on mobility parameters,
providing guidance for controlling contagion spread by constraining mobility
processes. We recover the threshold behavior by analyzing diffusion processes
mediated by real human commuting data.Comment: 20 pages of Main Text including 4 figures, 7 pages of Supplementary
Information; Nature Physics (2011
Simulation of an SEIR infectious disease model on the dynamic contact network of conference attendees
The spread of infectious diseases crucially depends on the pattern of
contacts among individuals. Knowledge of these patterns is thus essential to
inform models and computational efforts. Few empirical studies are however
available that provide estimates of the number and duration of contacts among
social groups. Moreover, their space and time resolution are limited, so that
data is not explicit at the person-to-person level, and the dynamical aspect of
the contacts is disregarded. Here, we want to assess the role of data-driven
dynamic contact patterns among individuals, and in particular of their temporal
aspects, in shaping the spread of a simulated epidemic in the population.
We consider high resolution data of face-to-face interactions between the
attendees of a conference, obtained from the deployment of an infrastructure
based on Radio Frequency Identification (RFID) devices that assess mutual
face-to-face proximity. The spread of epidemics along these interactions is
simulated through an SEIR model, using both the dynamical network of contacts
defined by the collected data, and two aggregated versions of such network, in
order to assess the role of the data temporal aspects.
We show that, on the timescales considered, an aggregated network taking into
account the daily duration of contacts is a good approximation to the full
resolution network, whereas a homogeneous representation which retains only the
topology of the contact network fails in reproducing the size of the epidemic.
These results have important implications in understanding the level of
detail needed to correctly inform computational models for the study and
management of real epidemics
Predictability and epidemic pathways in global outbreaks of infectious diseases: the SARS case study
Background: The global spread of the severe acute respiratory syndrome (SARS)
epidemic has clearly shown the importance of considering the long-range
transportation networks in the understanding of emerging diseases outbreaks.
The introduction of extensive transportation data sets is therefore an
important step in order to develop epidemic models endowed with realism.
Methods: We develop a general stochastic meta-population model that
incorporates actual travel and census data among 3 100 urban areas in 220
countries. The model allows probabilistic predictions on the likelihood of
country outbreaks and their magnitude. The level of predictability offered by
the model can be quantitatively analyzed and related to the appearance of
robust epidemic pathways that represent the most probable routes for the spread
of the disease. Results: In order to assess the predictive power of the model,
the case study of the global spread of SARS is considered. The disease
parameter values and initial conditions used in the model are evaluated from
empirical data for Hong Kong. The outbreak likelihood for specific countries is
evaluated along with the emerging epidemic pathways. Simulation results are in
agreement with the empirical data of the SARS worldwide epidemic. Conclusions:
The presented computational approach shows that the integration of long-range
mobility and demographic data provides epidemic models with a predictive power
that can be consistently tested and theoretically motivated. This computational
strategy can be therefore considered as a general tool in the analysis and
forecast of the global spreading of emerging diseases and in the definition of
containment policies aimed at reducing the effects of potentially catastrophic
outbreaks.Comment: 21 pages, 2 tables, 7 figure
Global response to pandemic flu: more research needed on a critical front
If and when sustained human-to-human transmission of H5N1 becomes a reality, the world will no longer be dealing with sporadic avian flu borne along migratory flight paths of birds, but aviation flu – winged at subsonic speed along commercial air conduits to every corner of planet Earth. Given that air transportation is the one feature that most differentiates present day transmission scenarios from those in 1918, our present inability to prevent spread of influenza by international air travel, as reckoned by the World Health Organization, constitutes a major weakness in the current global preparedness plan against pandemic flu. Despite the lessons of SARS, it is surprising that aviation-related health policy options have not been more rigorously evaluated, or scientific research aimed at strengthening public health measures on the air transportation front, more energetically pursued
Desarrollo, subjetividad y transgresiones identitarias en las costas del sur- austral chileno
This work is part of an investigation into the contemporary dynamics of development and modernization in the southern and far southern coastal areas of Chile, specifically the shoreline of the northern part of the Aysen Region. The objective is to propose a theoretical-conceptual reflection to enable ethnographic data to be framed as a problem and interpreted as a function of a political reading which - why not say so? - could transform the world of the southern and far southern coastal zone. The central argument of the text is hypothetical: the dilemmas of development, in the current circumstances of the coasts of the Aysen Region, are susceptible of resolution (at least up to a point) from a conscious, reflexive change of perspective on culture as the word is understood in anthropology. Este trabajo se enmarca en una investigación sobre las dinámicas contemporáneas del desarrollo y la modernización en las costas sur-australes de Chile, específicamente en el litoral norte de la región de Aisén. A partir de un conjunto de datos etnográficos se propone una reflexión teórico-conceptual que permita problematizar e interpretar esos datos en función de una lectura política y, por qué no decirlo, transformadora del mundo costero sur-austral. El argumento central del texto tiene carácter hipotético: las encrucijadas del desarrollo, en las actuales coyunturas de las costas aiseninas, son susceptibles de ser resueltas (al menos hasta cierto punto) a partir de un giro reflexivo y consciente sobre eso que en antropología llamamos cultura
Evaluating Temporal Factors in Combined Interventions of Workforce Shift and School Closure for Mitigating the Spread of Influenza
10.1371/journal.pone.0032203PLoS ONE7
Controlling Pandemic Flu: The Value of International Air Travel Restrictions
BACKGROUND: Planning for a possible influenza pandemic is an extremely high priority, as social and economic effects of an unmitigated pandemic would be devastating. Mathematical models can be used to explore different scenarios and provide insight into potential costs, benefits, and effectiveness of prevention and control strategies under consideration. METHODS AND FINDINGS: A stochastic, equation-based epidemic model is used to study global transmission of pandemic flu, including the effects of travel restrictions and vaccination. Economic costs of intervention are also considered. The distribution of First Passage Times (FPT) to the United States and the numbers of infected persons in metropolitan areas worldwide are studied assuming various times and locations of the initial outbreak. International air travel restrictions alone provide a small delay in FPT to the U.S. When other containment measures are applied at the source in conjunction with travel restrictions, delays could be much longer. If in addition, control measures are instituted worldwide, there is a significant reduction in cases worldwide and specifically in the U.S. However, if travel restrictions are not combined with other measures, local epidemic severity may increase, because restriction-induced delays can push local outbreaks into high epidemic season. The per annum cost to the U.S. economy of international and major domestic air passenger travel restrictions is minimal: on the order of 0.8% of Gross National Product. CONCLUSIONS: International air travel restrictions may provide a small but important delay in the spread of a pandemic, especially if other disease control measures are implemented during the afforded time. However, if other measures are not instituted, delays may worsen regional epidemics by pushing the outbreak into high epidemic season. This important interaction between policy and seasonality is only evident with a global-scale model. Since the benefit of travel restrictions can be substantial while their costs are minimal, dismissal of travel restrictions as an aid in dealing with a global pandemic seems premature
On the Treatment of Airline Travelers in Mathematical Models
The global spread of infectious diseases is facilitated by the ability of infected humans to travel thousands of miles in short time spans, rapidly transporting pathogens to distant locations. Mathematical models of the actual and potential spread of specific pathogens can assist public health planning in the case of such an event. Models should generally be parsimonious, but must consider all potentially important components of the system to the greatest extent possible. We demonstrate and discuss important assumptions relative to the parameterization and structural treatment of airline travel in mathematical models. Among other findings, we show that the most common structural treatment of travelers leads to underestimation of the speed of spread and that connecting travel is critical to a realistic spread pattern. Models involving travelers can be improved significantly by relatively simple structural changes but also may require further attention to details of parameterization