Seyed Moghadas

Publications (20)11.34 Total impact

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  Available from: PubMed Central

  Article: Variability in transmissibility of the 2009 H1N1 pandemic in Canadian communities.

  Luiz C Mostaço-Guidolin, Amy Greer, Beate Sander, Jianhong Wu, Seyed M Moghadas
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  ABSTRACT: The prevalence and severity of the 2009 H1N1 pandemic appeared to vary significantly across populations and geographic regions. We sought to investigate the variability in transmissibility of H1N1 pandemic in different health regions (including urban centres and remote, isolated communities) in the province of Manitoba, Canada. The Richards model was used to fit to the daily number of laboratory-confirmed cases and estimate transmissibility (referred to as the basic reproduction number, R0), doubling times, and turning points of outbreaks in both spring and fall waves of the H1N1 pandemic in several health regions. We observed considerable variation in R0 estimates ranging from 1.55 to 2.24, with confidence intervals ranging from 1.45 to 2.88, for an average generation time of 2.9 days, and shorter doubling times in some remote and isolated communities compared to urban centres, suggesting a more rapid spread of disease in these communities during the first wave. For the second wave, Re, the effective reproduction number, is estimated to be lower for remote and isolated communities; however, outbreaks appear to have been driven by somewhat higher transmissibility in urban centres. There was considerable geographic variation in transmissibility of the 2009 pandemic outbreaks. While highlighting the importance of estimating R0 for informing health responses, the findings indicate that projecting the transmissibility for large-scale epidemics may not faithfully characterize the early spread of disease in remote and isolated communities.
  BMC Research Notes 12/2011; 4:537.
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  Available from: Amy L Greer

  Article: Estimated epidemiologic parameters and morbidity associated with pandemic H1N1 influenza.

  Ashleigh R Tuite, Amy L Greer, Michael Whelan, Anne-Luise Winter, Brenda Lee, Ping Yan, Jianhong Wu, Seyed Moghadas, David Buckeridge, Babak Pourbohloul, David N Fisman
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  ABSTRACT: In the face of an influenza pandemic, accurate estimates of epidemiologic parameters are required to help guide decision-making. We sought to estimate epidemiologic parameters for pandemic H1N1 influenza using data from initial reports of laboratory-confirmed cases. We obtained data on laboratory-confirmed cases of pandemic H1N1 influenza reported in the province of Ontario, Canada, with dates of symptom onset between Apr. 13 and June 20, 2009. Incubation periods and duration of symptoms were estimated and fit to parametric distributions. We used competing-risk models to estimate risk of hospital admission and case-fatality rates. We used a Markov Chain Monte Carlo model to simulate disease transmission. The median incubation period was 4 days and the duration of symptoms was 7 days. Recovery was faster among patients less than 18 years old than among older patients (hazard ratio 1.23, 95% confidence interval 1.06-1.44). The risk of hospital admission was 4.5% (95% CI 3.8%-5.2%) and the case-fatality rate was 0.3% (95% CI 0.1%-0.5%). The risk of hospital admission was highest among patients less than 1 year old and those 65 years or older. Adults more than 50 years old comprised 7% of cases but accounted for 7 of 10 initial deaths (odds ratio 28.6, 95% confidence interval 7.3-111.2). From the simulation models, we estimated the following values (and 95% credible intervals): a mean basic reproductive number (R0, the number of new cases created by a single primary case in a susceptible population) of 1.31 (1.25-1.38), a mean latent period of 2.62 (2.28-3.12) days and a mean duration of infectiousness of 3.38 (2.06-4.69) days. From these values we estimated a serial interval (the average time from onset of infectiousness in a case to the onset of infectiousness in a person infected by that case) of 4-5 days. The low estimates for R0 indicate that effective mitigation strategies may reduce the final epidemic impact of pandemic H1N1 influenza.
  Canadian Medical Association Journal 12/2009; 182(2):131-6. · 8.22 Impact Factor
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  Available from: PubMed Central

  Article: Antiviral resistance during pandemic influenza: implications for stockpiling and drug use.

  Julien Arino, Christopher S Bowman, Seyed M Moghadas
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  ABSTRACT: The anticipated extent of antiviral use during an influenza pandemic can have adverse consequences for the development of drug resistance and rationing of limited stockpiles. The strategic use of drugs is therefore a major public health concern in planning for effective pandemic responses. We employed a mathematical model that includes both sensitive and resistant strains of a virus with pandemic potential, and applies antiviral drugs for treatment of clinical infections. Using estimated parameters in the published literature, the model was simulated for various sizes of stockpiles to evaluate the outcome of different antiviral strategies. We demonstrated that the emergence of highly transmissible resistant strains has no significant impact on the use of available stockpiles if treatment is maintained at low levels or the reproduction number of the sensitive strain is sufficiently high. However, moderate to high treatment levels can result in a more rapid depletion of stockpiles, leading to run-out, by promoting wide-spread drug resistance. We applied an antiviral strategy that delays the onset of aggressive treatment for a certain amount of time after the onset of the outbreak. Our results show that if high treatment levels are enforced too early during the outbreak, a second wave of infections can potentially occur with a substantially larger magnitude. However, a timely implementation of wide-scale treatment can prevent resistance spread in the population, and minimize the final size of the pandemic. Our results reveal that conservative treatment levels during the early stages of the outbreak, followed by a timely increase in the scale of drug-use, will offer an effective strategy to manage drug resistance in the population and avoid run-out. For a 1918-like strain, the findings suggest that pandemic plans should consider stockpiling antiviral drugs to cover at least 20% of the population.
  BMC Infectious Diseases 02/2009; 9:8. · 3.12 Impact Factor
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  Available from: Gergely Röst

  Article: Post-exposure prophylaxis during pandemic outbreaks

  Seyed Moghadas, Christopher Bowman, Gergely Röst, David Fisman, Jianhong Wu
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  ABSTRACT: Abstract Background With the rise of the second pandemic wave of the novel influenza A (H1N1) virus in the current season in the Northern Hemisphere, pandemic plans are being carefully re-evaluated, particularly for the strategic use of antiviral drugs. The recent emergence of oseltamivir-resistant in treated H1N1 patients has raised concerns about the prudent use of neuraminidase inhibitors for both treatment of ill individuals and post-exposure prophylaxis of close contacts. Methods We extended an established population dynamical model of pandemic influenza with treatment to include post-exposure prophylaxis of close contacts. Using parameter estimates published in the literature, we simulated the model to evaluate the combined effect of treatment and prophylaxis in minimizing morbidity and mortality of pandemic infections in the context of transmissible drug resistance. Results We demonstrated that, when transmissible resistant strains are present, post-exposure prophylaxis can promote the spread of resistance, especially when combined with aggressive treatment. For a given treatment level, there is an optimal coverage of prophylaxis that minimizes the total number of infections (final size) and this coverage decreases as a higher proportion of infected individuals are treated. We found that, when treatment is maintained at intermediate levels, limited post-exposure prophylaxis provides an optimal strategy for reducing the final size of the pandemic while minimizing the total number of deaths. We tested our results by performing a sensitivity analysis over a range of key model parameters and observed that the incidence of infection depends strongly on the transmission fitness of resistant strains. Conclusion Our findings suggest that, in the presence of transmissible drug resistance, strategies that prioritize the treatment of only ill individuals, rather than the prophylaxis of those suspected of being exposed, are most effective in reducing the morbidity and mortality of the pandemic. The impact of post-exposure prophylaxis depends critically on the treatment level and the transmissibility of resistant strains and, therefore, enhanced surveillance and clinical monitoring for resistant mutants constitutes a key component of any comprehensive plan for antiviral drug use during an influenza pandemic.
  BMC Medicine. 01/2009;
• Article: The impact of prophylaxis of healthcare workers on influenza pandemic burden

  M. Gardam, D Liang, Seyed Moghadas, J Wu, Q Zeng, H Zhu
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  Available from: watam.org

  Article: Bifurcation and numerical analysis of a generalized Gause-type predator-prey model

  Seyed Moghadas, M. Alexander
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• Article: Neimark-Sacker bifurcations in a non-standard numerical scheme for a class of positivity-preserving ODEs

  M. Alexander, Arthur Summers, Seyed Moghadas
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  Available from: Abba B Gumel

  Article: Could condoms stop the AIDS epidemic?

  Seyed Moghadas, Abba Gumel, Robert McLeod, R. Gordon
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• Article: A vaccination model for transmission dynamics of influenza

  M. Alexander, Christopher Bowman, Seyed Moghadas, Abba Gumel, B. Sahai, Arthur Summers
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• Article: Periodicity in an epidemic model with generalized nonlinear incidence

  M. Alexander, Seyed Moghadas
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• Article: Waning herd immunity: a challenge for eradication of measles

  Seyed Moghadas, M. Alexander, B. Sahai
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• Article: Management of drug-resistance in the population: influenza as a case study

  Seyed Moghadas
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• Article: A delay differential model for pandemic influenza with antiviral treatment

  M. Alexander, Seyed Moghadas, G. R�?st, J Wu
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• Article: Prophylaxis of healthcare workers in an influenza pandemic

  Seyed Moghadas
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• Article: Bifurcation analysis of an SIRS epidemic model with generalized incidence

  M. Alexander, Seyed Moghadas
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  Available from: impa.br

  Article: {IO(l)} shift in Hopf bifurcation for a class of non-standard numerical schemes

  M. Alexander, Seyed Moghadas
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• Article: Population-wide emergence of antiviral resistance during pandemic influenza

  Seyed Moghadas, Christopher Bowman, G. R�?st, J Wu
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• Article: Emergence of drug resistance: implications for antiviral control of pandemic influenza

  M. Alexander, Christopher Bowman, Z Feng, M. Gardam, Seyed Moghadas, G. Rost, J Wu, P. Yan
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• Article: A positivity-preserving Mickens discretization of an epidemic model

  Seyed Moghadas, M. Alexander, Brian Corbett, Abba Gumel
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  Available from: nrc-cnrc.gc.ca

  Article: Strategies for the use of oseltamivir and zanamivir during pandemic outbreaks

  Elsa Hansen, Troy Day, Julien Arino, Jianhong Wu, Seyed M Moghadas, Seyed Moghadas
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  ABSTRACT: BACKGROUND: The use of neuraminidase inhibitors (oseltamivir and zanamivir) for the treatment of ill individuals has been an important intervention during the 2009 H1N1 pandemic. However, the emergence and spread of drug resistance remains a major concern and, therefore, optimizing antiviral strategies is crucial to retain the long-term effectiveness of these pharmaceutical interventions. METHODS: A dynamic model of disease transmission was developed to investigate optimal scenarios for the use of a secondary drug (eg, zanamivir). Considering both small and large stockpiles, attack rates were projected by simulating the model to identify 'tipping points' for switching to zanamivir as resistance to oseltamivir develops. RESULTS: The use of a limited stockpile of zanamivir can substantially reduce the overall attack rate during pandemic outbreaks. For a reasonably large stockpile of zanamivir, it is optimal to delay the use of this drug for a certain amount of time during which oseltamivir is used as the primary drug. For smaller stockpiles, however, earlier use of zanamivir will be most effective in reducing the overall attack rate. Given a limited stockpile of zanamivir (1.8% in the Canadian plan) without replenishment, and assuming that the fraction of ill individuals being treated is maintained below 60%, the results suggest that zanamivir should be dispensed as the primary drug for thresholds of the cumulative number of oseltamivir resistance below 20%. INTERPRETATION: Strategic use of a secondary drug becomes crucial for pandemic mitigation if vaccination and other interventions fail to sufficiently reduce disease transmission in the community. These findings highlight the importance of enhanced surveillance and clinical monitoring for rapid identification of resistance emergence and its population incidence, so that optimal timing for adaptation to the use of drugs can be achieved. yes yes Open access - free to all