540 research outputs found
Theoretical basis to measure the impact of short-lasting control of an infectious disease on the epidemic peak
Background. While many pandemic preparedness plans have promoted disease control effort to lower and delay an epidemic peak, analytical methods for determining the required control effort and making statistical inferences have yet to be sought. As a first step to address this issue, we present a theoretical basis on which to assess the impact of an early intervention on the epidemic peak, employing a simple epidemic model. Methods. We focus on estimating the impact of an early control effort (e.g. unsuccessful containment), assuming that the transmission rate abruptly increases when control is discontinued. We provide analytical expressions for magnitude and time of the epidemic peak, employing approximate logistic and logarithmic-form solutions for the latter. Empirical influenza data (H1N1-2009) in Japan are analyzed to estimate the effect of the summer holiday period in lowering and delaying the peak in 2009. Results. Our model estimates that the epidemic peak of the 2009 pandemic was delayed for 21 days due to summer holiday. Decline in peak appears to be a nonlinear function of control-associated reduction in the reproduction number. Peak delay is shown to critically depend on the fraction of initially immune individuals. Conclusions. The proposed modeling approaches offer methodological avenues to assess empirical data and to objectively estimate required control effort to lower and delay an epidemic peak. Analytical findings support a critical need to conduct population-wide serological survey as a prior requirement for estimating the time of peak. © 2011 Omori and Nishiura; licensee BioMed Central Ltd.published_or_final_versio
An analysis of target recipient groups for monovalent 2009 pandemic influenza vaccine and trivalent seasonal influenza vaccines in 2009-10 and 2010-11
Poster Presentation: SPA5 - How to Evaluate Vaccine Effectiveness and Efficacy?: abstract no. A513PINTRODUCTION: Vaccination is generally considered to be the best primary prevention measure against influenza virus infection. Many countries encourage specific target groups of people to undertake vaccination, often with financial subsidies or a list of priority. To understand differential patterns of national target groups for influenza vaccination before, during and after the 2009 influenza pandemic, we reviewed and identified changes in national target groups for trivalent seasonal influenza and the monovalent 2009 pandemic influenza vaccines dur...postprin
Dynamical effects of interactions and the Tully-Fisher relation for Hickson compact groups
We investigate the properties of the B-band Tully-Fisher (T-F) relation for
25 compact group galaxies, using Vmax derived from 2-D velocity maps. Our main
result is that the majority of the Hickson Compact Group galaxies lie on the
T-F relation. However, about 20% of the galaxies, including the lowest-mass
systems, have higher B luminosities for a given mass, or alternatively, a mass
which is too low for their luminosities. We favour a scenario in which outliers
have been brightened due to either enhanced star formation or merging.
Alternatively, the T-F outliers may have undergone truncation of their dark
halo due to interactions. It is possible that in some cases, both effects
contribute. The fact that the B-band T-F relation is similar for compact group
and field galaxies tells us that these galaxies show common mass-to-size
relations and that the halos of compact group galaxies have not been
significantly stripped inside R25. We find that 75% of the compact group
galaxies studied (22 out of 29) have highly peculiar velocity fields.
Nevertheless, a careful choice of inclination, position angle and center,
obtained from the velocity field, and an average of the velocities over a large
sector of the galaxy enabled the determination of fairly well-behaved rotation
curves for the galaxies. However, two of the compact group galaxies which are
the most massive members in M51--like pairs, HCG 91a and HCG 96a, have very
asymmetric rotation curves, with one arm rising and the other one falling,
indicating, most probably, a recent perturbation by the small close companions.Comment: 15 pages, 4 figures, accepted for publication in the Astronomical
Journa
Pros and cons of estimating the reproduction number from early epidemic growth rate of influenza A (H1N1) 2009
<p>Abstract</p> <p>Background</p> <p>In many parts of the world, the exponential growth rate of infections during the initial epidemic phase has been used to make statistical inferences on the reproduction number, <it>R</it>, a summary measure of the transmission potential for the novel influenza A (H1N1) 2009. The growth rate at the initial stage of the epidemic in Japan led to estimates for <it>R </it>in the range 2.0 to 2.6, capturing the intensity of the initial outbreak among school-age children in May 2009.</p> <p>Methods</p> <p>An updated estimate of <it>R </it>that takes into account the epidemic data from 29 May to 14 July is provided. An age-structured renewal process is employed to capture the age-dependent transmission dynamics, jointly estimating the reproduction number, the age-dependent susceptibility and the relative contribution of imported cases to secondary transmission. Pitfalls in estimating epidemic growth rates are identified and used for scrutinizing and re-assessing the results of our earlier estimate of <it>R</it>.</p> <p>Results</p> <p>Maximum likelihood estimates of <it>R </it>using the data from 29 May to 14 July ranged from 1.21 to 1.35. The next-generation matrix, based on our age-structured model, predicts that only 17.5% of the population will experience infection by the end of the first pandemic wave. Our earlier estimate of <it>R </it>did not fully capture the population-wide epidemic in quantifying the next-generation matrix from the estimated growth rate during the initial stage of the pandemic in Japan.</p> <p>Conclusions</p> <p>In order to quantify <it>R </it>from the growth rate of cases, it is essential that the selected model captures the underlying transmission dynamics embedded in the data. Exploring additional epidemiological information will be useful for assessing the temporal dynamics. Although the simple concept of <it>R </it>is more easily grasped by the general public than that of the next-generation matrix, the matrix incorporating detailed information (e.g., age-specificity) is essential for reducing the levels of uncertainty in predictions and for assisting public health policymaking. Model-based prediction and policymaking are best described by sharing fundamental notions of heterogeneous risks of infection and death with non-experts to avoid potential confusion and/or possible misuse of modelling results.</p
Monitoring RXTE Observations of Markarian 348: the origin of the column density variations
We analyze 37 RXTE observations of the type 2 Seyfert galaxy Mrk348 obtained
during a period of 14 months. We confirm the spectral variability previous
reported by Smith et al., in the sense that thecolumn density decreases by a
factor of ~3 as the count rate increases. Column density variations could
possibly originate either due to the random drift of clouds within the
absorption screen, or due to photoionization processes. Our modeling of the
observed variations implies that the first scenario is more likely. These
clouds should lie in a distance of >2 light years from the source, having a
diameter of a few light days and a density of >10^7 cm^(-3), hence probably
residing outside the Broad Line Region.Comment: 6 pages, 3 figures, to appear in MNRA
Universal Texture of Quark and Lepton Mass Matrices and a Discrete Symmetry Z_3
Recent neutrino data have been favourable to a nearly bimaximal mixing, which
suggests a simple form of the neutrino mass matrix. Stimulated by this matrix
form, a possibility that all the mass matrices of quarks and leptons have the
same form as in the neutrinos is investigated. The mass matrix form is
constrained by a discrete symmetry Z_3 and a permutation symmetry S_2. The
model, of course, leads to a nearly bimaximal mixing for the lepton sectors,
while, for the quark sectors, it can lead to reasonable values of the CKM
mixing matrix and masses.Comment: 24 pages, RevTEX, no figure, some references and comments were adde
SO(10) GUT and Quark-Lepton Mass Matrices
The phenomenological model that all quark and lepton mass matrices have the
same zero texture, namely their (1,1), (1,3) and (3,1) components are zeros, is
discussed in the context of SO(10) Grand Unified Theories (GUTs). The mass
matrices of type I for quarks are consistent with the experimental data in the
quark sector. For the lepton sector, consistent fitting to the data of neutrino
oscillation experiments force us to use the mass matrix for the charged leptons
which is slightly deviated from type I. Given quark masses and charged lepton
masses, the model includes 19 free parameters, whereas the SO(10) GUTs gives 16
constrained equations. Changing the remaining three parameters freely, we can
fit all the entries of the CKM quark mixing matrix and the MNS lepton mixing
matrix, and three neutrino masses consistently with the present experimental
data.Comment: 32pp, REV TeX, 12 EPS Figure
Extracting key information from historical data to quantify the transmission dynamics of smallpox
<p>Abstract</p> <p>Background</p> <p>Quantification of the transmission dynamics of smallpox is crucial for optimizing intervention strategies in the event of a bioterrorist attack. This article reviews basic methods and findings in mathematical and statistical studies of smallpox which estimate key transmission parameters from historical data.</p> <p>Main findings</p> <p>First, critically important aspects in extracting key information from historical data are briefly summarized. We mention different sources of heterogeneity and potential pitfalls in utilizing historical records. Second, we discuss how smallpox spreads in the absence of interventions and how the optimal timing of quarantine and isolation measures can be determined. Case studies demonstrate the following. (1) The upper confidence limit of the 99th percentile of the incubation period is 22.2 days, suggesting that quarantine should last 23 days. (2) The highest frequency (61.8%) of secondary transmissions occurs 3–5 days after onset of fever so that infected individuals should be isolated before the appearance of rash. (3) The U-shaped age-specific case fatality implies a vulnerability of infants and elderly among non-immune individuals. Estimates of the transmission potential are subsequently reviewed, followed by an assessment of vaccination effects and of the expected effectiveness of interventions.</p> <p>Conclusion</p> <p>Current debates on bio-terrorism preparedness indicate that public health decision making must account for the complex interplay and balance between vaccination strategies and other public health measures (e.g. case isolation and contact tracing) taking into account the frequency of adverse events to vaccination. In this review, we summarize what has already been clarified and point out needs to analyze previous smallpox outbreaks systematically.</p
Early Epidemiological Assessment of the Virulence of Emerging Infectious Diseases: A Case Study of an Influenza Pandemic
Background: The case fatality ratio (CFR), the ratio of deaths from an infectious disease to the number of cases, provides an assessment of virulence. Calculation of the ratio of the cumulative number of deaths to cases during the course of an epidemic tends to result in a biased CFR. The present study develops a simple method to obtain an unbiased estimate of confirmed CFR (cCFR), using only the confirmed cases as the denominator, at an early stage of epidemic, even when there have been only a few deaths. Methodology/Principal Findings: Our method adjusts the biased cCFR by a factor of underestimation which is informed by the time from symptom onset to death. We first examine the approach by analyzing an outbreak of severe acute respiratory syndrome in Hong Kong (2003) with known unbiased cCFR estimate, and then investigate published epidemiological datasets of novel swine-origin influenza A (H1N1) virus infection in the USA and Canada (2009). Because observation of a few deaths alone does not permit estimating the distribution of the time from onset to death, the uncertainty is addressed by means of sensitivity analysis. The maximum likelihood estimate of the unbiased cCFR for influenza may lie in the range of 0.16-4.48% within the assumed parameter space for a factor of underestimation. The estimates for influenza suggest that the virulence is comparable to the early estimate in Mexico. Even when there have been no deaths, our model permits estimating a conservative upper bound of the cCFR. Conclusions: Although one has to keep in mind that the cCFR for an entire population is vulnerable to its variations among sub-populations and underdiagnosis, our method is useful for assessing virulence at the early stage of an epidemic and for informing policy makers and the public. © 2009 Nishiura et al.published_or_final_versio
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