Article

Modeling age- and time-specific incidence from seroprevalence: Toxoplasmosis

Epidemiology and Biostatistics Unit, Division of Public Health, Institute of Child Health, London.
American Journal of Epidemiology (Impact Factor: 5.23). 06/1993; 137(9):1022-34.
Source: PubMed

ABSTRACT

New forms of catalytic epidemic models were developed to estimate the incidence of primary toxoplasmosis infection from age- and time-specific seroprevalence data collected from persons aged 0-100 years in South Yorkshire, England, 1969-1990. Piecewise constant and exponential polynomial functions were used to assess the way in which incidence depended on age and time, and to guide the choice of parametric models suitable for prediction. Incidence estimates were biased unless both age- and time-dependence were allowed for. New findings on the epidemiology of this infection emerged. Incidence appears to have fallen sixfold between 1915 and 1970, but has remained stable for the last 20 years. There is a marked peak in incidence in childhood. The incidence throughout the childbearing period is currently estimated to be 0.07 or less per 100 susceptible persons per year. However, these predictions were highly sensitive to assumptions about incidence in childhood, and the 95% confidence limits for a range of models were between 0.003 and 0.32% per year. Age- and time-specific seroprevalence data can be collected inexpensively on a mass population basis, and, with appropriate incidence modeling, may prove to be a powerful method for the study of infectious disease and for incidence prediction.

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    • "at which the infection is contracted is a key variable affecting the clinical foetal outcome (Ades & Nokes, 1993; Lopez et al., 2000; Martin, 2001). While the prevalence rates of T. gondii were up to 50-80% in Central and South American as well as some European populations, primary infection with T. gondii in pregnant women occurs all over the world with frequencies between 0.1-1% (Stray-Pedersen, 1993). "

    Full-text · Dataset · Apr 2013
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    • "Cross-sectional and longitudinal surveys of pathogen-specific antibody levels provide valuable data for assessment of infection dynamics, especially when combined with information on age to provide age serological profiles (e.g. [5] [6] [7]). The immunity level of an individual is determined by measurement of the concentration of specific antibodies to the pathogen in a sample of serum or, more recently, oral fluid ('saliva'). "
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    ABSTRACT: Assessment of immunological status is a powerful tool in the surveillance and control of infectious pathogens in livestock and human populations. The distribution of immunity levels in the population provides information on time and age dependent transmission. A stochastic model is developed for a livestock population which relates the dynamics of the distribution of immunity levels at the population level to those of pathogen transmission. A general model with K immunity level categories is first proposed, taking into account the increase of the immunity level due to an infection or a re-exposure, the decrease of the immunity level with time since infection or exposure, and the effect of immunity level on the susceptibility and the infectivity of individuals. Numerical results are presented in the particular cases with K=2 and K=3 immunity level categories. We demonstrate that for a given distribution of the immunity levels at the population level, the model can be used to identify quantities such as most likely periods of time since introduction of infection. We discuss this approach in relation to analysis of serological data.
    Full-text · Article · Apr 2006 · Mathematical Biosciences
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    • "at which the infection is contracted is a key variable affecting the clinical foetal outcome (Ades & Nokes, 1993; Lopez et al., 2000; Martin, 2001). While the prevalence rates of T. gondii were up to 50-80% in Central and South American as well as some European populations, primary infection with T. gondii in pregnant women occurs all over the world with frequencies between 0.1-1% (Stray-Pedersen, 1993). "

    Full-text · Article · Jan 2006
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