Talk Titles and Abstracts
Odo Diekmann (Mathematical Institute, Utrecht University)
Inference concerning the spread of antibiotic resistant bacteria
in ICU (Intensive Care Units)
In order to estimate the relative importance of acquisition routes,
one can analyse data in the context of a Markov chain model. In
the lecture I will explain how one can combine data about admission,
discharge and the results of tests, with a stochastic model for
transmission and next perform Maximum Likelihood Estimation. This
is based on joint work with Martin Bootsma and Marc Bonten, see
http://www.math.uu.nl/people/koval/nwo/index.htm for more information
about the interdisciplinary project and a preprint version of the
paper M.C.J. Bootsma, Bonten, M.J.M., Nijssen, A.C. Fluit, and O.
Diekmann: An algorithm for real-time monitoring of bacterial transmission
routes in hospital settings.
Am. J. Epid. 166 (2007) 841-851 DOI : 10.1093/aje/kwm149.
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Zhilan Feng (Purdue University)
Modeling the evolutionary implications of influenza medication
strategies
Medication and treatment are important measures for prevention
and control of influenza. However, the benefit of antiviral use
can be compromised if drug-resistant strains arise. Consequently,
not only the epidemic size may increase with a higher level of treatment
but also the viruses may become more resistant to the antiviral
drugs. We use a mathematical model to explore the impact of antiviral
treatment on the transmission dynamics of influenza. The model includes
both drug-sensitive and -resistant strains.
Analytical and numerical results of the model show that the conventional
quantity for the control reproduction number is not appropriate
to use for gaining insights into the disease dynamics. We derive
a new reproduction number by considering multiple generations of
infection, and demonstrate that this new reproduction number provides
a more reasonable measure for evaluating control programs as well
as evolutionary implications of influenza medication strategies.
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John Glasser (Centers for Disease Control and Prevention)
Modeling the potential impact of heterogeneity in vaccine coverage
due to religious and philosophical exemptions
Using the simplest meta-population model capable of informing vaccination
policy, we have demonstrated that heterogeneity in vaccine coverage
increases the population-immunity threshold (below which outbreaks
will occur on the introduction of an infectious person), especially
when sub-populations mix non-randomly. Insofar as children with
religious or philosophical exemptions not only live in the same
households or neighborhoods, or attend the same schools, but also
associate preferentially with other children having like-minded
parents, non-medical exemptions reduce our ability to prevent outbreaks
of vaccine-preventable diseases disproportionately (i.e., more than
randomly distributed and mixed susceptible people do). By virtue
of higher reproduction numbers or lower vaccine efficacy, some diseases
are closer to the random mixing threshold than others. Among measles,
mumps and rubella, for example, mumps is closest, followed in turn
by measles and rubella, and immunity to mumps may wane absent boosting.
Travelers infected abroad who still harbor the pathogens responsible
for these diseases on returning to the US may cause outbreaks where
immunity is heterogeneous or mixing non-random. Thus, despite average
two-dose coverage of the measles, mumps and rubella vaccine above
90%, the mumps outbreaks on residential college campuses in the
rural mid-west during 2006 and 2009, and ongoing within an orthodox
Jewish community in the northeast, might have been expected in retrospect.
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Ying-Hen Hsieh (China Medical University)
Transmission Heterogeneity of 2009 pH1N1 in Central Taiwan:
Some Preliminary Results
A sero-epidemiology study was carried out in one urban city (Taichung
city) and one rural county (Nantou) in central Taiwan starting before
the 2008 fall influenza season in Taiwan and through the beginning
of 2010. Households with schoolchildren were recruited for the study
and followed sequentially, with serum samples were taken in several
pre-season and post-season sampling periods for haemagglutination
inhibition (HI) assay against H1N1 viruses of seasonal vaccine,
wild- type, and pH1N1 strains. Survey questionnaires regarding their
contact patterns, social demographic characteristics, and influenza-like
symptoms during the flu seasons are obtained. Using serologic evidence
of infection, i.e., 4-fold increase in HI titers, we investigate
the temporal changes in pH1N1 infections among this cohort, as well
as transmission heterogeneity due to age, household type/size, location,
status of vaccination, etc.
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Gauthier Sallet (INRIA & IRD)
Differential susceptibility and infectivity. Application to
transmission of HBV in Subsaharian Africa
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Beate Sander RN, MBA, MEcDev1,2,3, Chris T. Bauch PhD3,4, David
Fisman MD MPH5, Robert A. Fowler MD MSc3,6, Jeffrey C. Kwong MD
MSc5,7,8, Andreas Maetzel MD, PhD9, Allison McGeer MD10, Janet Raboud
PhD5,10, Damon Scales MD PhD6,11, Marija Zivkovic Gojovic MSc3,
and Murray Krahn MD MSc3,10,11
Is a Mass Immunization Program for Pandemic (H1N1) 2009 Good
Value for Money? Evidence from the Canadian Experience
1 Department of Health Policy, Management and Evaluation, University
of Toronto, Toronto, Canada, 2 Division of Clinical Decision-Making
and Health Care Research, University Health Network, Toronto, Canada,
3 Toronto Health Economics and Technology Assessment Collaborative,
Toronto, Canada, 4 Department of Mathematics and Statistics, University
of Guelph, Guelph, Canada, 5 Dalla Lana School of Public Health,
University of Toronto, Toronto, Canada, 6 Department of Medicine
and Interdepartmental Division of Critical Care Medicine, Sunnybrook
Health Sciences Center, Toronto, Ontario, Canada, 7 Institute for
Clinical Evaluative Sciences, Toronto, Canada, 8 Department of Family
and Community Medicine, University of Toronto, Toronto, Canada,
9 Amgen (Europe) GmbH, Zug, Switzerland, 10 Division of Infectious
Diseases, University Health Network, Toronto, Canada, 10 Faculty
of Pharmacy, University of Toronto, Toronto, Canada, 11 Department
of Medicine, University of Toronto, Toronto, Canada
Background: In response to pandemic H1N1 influenza 2009 outbreak,
many jurisdictions undertook mass immunization programs. The objective
of this study was to determine the cost-effectiveness of the mass
H1N1 immunization program in Ontario, Canada's most populous province
(population 13,000,000).
Methods: A cost-utility analysis comparing the H1N1 mass immunization
program in Ontario to no intervention was performed from the health
care payer perspective. The economic evaluation is informed by a
simulation model of a pandemic H1N1 2009 outbreak in a city in Ontario.
Health outcomes measured included number of cases, number of deaths
and QALYs. Probabilities for health care resource use (office visits,
emergency department (ED) visits, hospitalizations) and deaths were
based on Ontario pandemic H1N1 surveillance data and administrative
data. Costs included immunization program cost and health care cost
for treating H1N1 cases and were drawn from Ontario administrative
data sources. Primary outcomes were quality adjusted life-years
(QALYs), costs in 2009 Canadian dollars, and cost per QALY gained
(incremental cost-effectiveness ratio [ICER]).
Results: We estimated that 4.1 million cases of symptomatic influenza
would have occurred (31.5% symptomatic attack rate) in the absence
of an immunization program. Our model predicted that 22% of symptomatic
cases, 22% of office and ED visits, 23% of hospitalizations, and
of 25% of death were prevented by the program. While the program
was costly (C$180,400,000), it was also highly cost effective at
C$9,400/QALY gained. Projections were most sensitive to the timing
of the immunization program and less sensitive to immunization program
cost and QALYs. In all deterministic sensitivity analyses the ICER
remained well below WHO thresholds for cost-effectiveness. Finally,
probabilistic sensitivity analysis showed the H1N1 mass immunization
program in Ontario to be cost-effective in all simulations (100%)
at a willingness-to-pay of $25,000 per QALY.
Conclusions:
This analysis suggests that a mass immunization program as carried
out in Ontario in response to H1N1 2009 was not only effective in
preventing influenza cases and health care resource use but was
also highly cost-effective despite the substantial program cost.
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Yiming Shao, M.D. & Ph. D. (National Center for AIDS/STD
Control and Prevention & China Center for Disease Control and
Prevention)
Progress, Challenge and New Strategy of AIDS Prevention and
Control in China
The HIV epidemics in China started among IDUs in border region
in late 1980s, followed by the 2nd wave in the paid plasma donors
in central China in the mid 1990s, and the 3rd wave of sexual transmission
at the turning of the century. Both hetero-sexual and homosexual
transmission have taken more than half of the total reported HIV
infections since 2007. Chinese government has launched an impressive
AIDS prevention campaign, with strong support from international
communities, and foundations such as Global Fund and the Gates Foundation.
Various intervention packages, including condom promotion, methadone
substitutions and needle exchange programs are conducted. Even though
a lot of progress has been made, the current AIDS control strategies
are still not effective enough to significantly block the epidemic
spreading from high risk groups to the general population. Most
all the best practices for AIDS prevention are developed by other
countries, which may not fit to the local environments and some
of the current programs are lacking long term sustainability. There
is urgent need to develop new strategies through research and international
collaboration addressing the scientific and policy challenges facing
China's AIDS control efforts.
The presentation will discuss some of the challenges and provide
examples of the type of researches needed to overcome those technical
obstacles. Those research areas include new techniques of measuring
the epidemic and its trends, a strategy to use HIV drug surveillance
data to support public health approach ART program, as well as using
mathematic model to design comprehensive and sustainable prevention,
treatment and care program, targeting both the epidemic and its
roots. Shown by the model's simulation the new strategy will lead
to effectively control the prevalence and incident of HIV/AIDS in
the high epidemic region within 10 years. Finally the presentation
will discuss the innovative research strategy moving HIV vaccine
design to clinical trials as well as how to strengthen national,
regional and international cooperation towards an effective vaccine.
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Yanni Xiao (School of Sciences, Xi'an Jiaotong University)
Community-based measures for mitigating the 2009 H1N1 pandemic
in China
During the 2009 A/H1N1 influenza pandemic, very strict interventions
including Fengxiao were taken in mainland China to prevent imported
cases and to slow down the spread to the community. How effective
the local control measures are remains to be assessed, and answers
to this question may inform decisions whether there should be enforced
and/or improved local control measures to mitigate the outbreak.
We estimated the mean reproduction number and analyzed the effect
of varying interventions on outbreak and attack rate by simulating
the spatially stratified compartmental model. We found that early
implementation of Fengxiao, although hardly avoid a global outbreak,
did and can substantially delay the outbreak peak time. Such a measure,
when coupled with other strong quarantine and hygiene precaution
measures, can reduce significantly the final size and outbreak peak
altogether. This finding strongly suggests that prompt interventions
including Fengxiao should be implemented to respond to future waves
and emerging epidemics in China.
Joint work with S. Tang, Y. Yang, Y. Zhou, J. Wu and Zima
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Dr. Xiaoqiang Zhao (Memorial University of Newfoundland)
A Tuberculosis Model with Seasonality
The statistical data of tuberculosis (TB) cases show seasonal fluctuations
in many countries. A TB model incorporating seasonality is developed
and the basic reproduction ratio is defined. It is shown that the
disease-free equilibrium is globally asymptotically stable and the
disease eventually disappears if the basic reproduction ratio is
less than one; and there exists at least one positive periodic solution
and the disease is uniformly persistent if this ratio is greater
than one. Numerical simulations indicate that in the latter case
there may be a unique positive periodic solution which is globally
asymptotically stable. Parameter values of the model are estimated
according to demographic and epidemiological data in China. The
simulation results are in good accordance with the seasonal variation
of the reported cases of active TB in China. This talk is based
on a joint work with Drs. Luju Liu and Yicang Zhou.
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