ISSN:0277-6715    

DOI:10.1002/sim.4780080103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThis article describes statistical methods for monitoring the epidemic of the acquired immunodeficiency syndrome (AIDS). A log‐linear model is proposed to estimate AIDS incidence and its growth rate while taking account of delays in case reporting. An empirical Bayes approach for estimating the epidemic growth rate in low prevalence subgroups is introduced. These methods are illustrated with an analysis of AIDS incidence trends for seven risk groups in each of six geographic regions using the Centers for Disease Control AIDS case registry data as of September 1987. The analysis finds that AIDS incidence is currently doubling about once every two years and that the relative composition of new cases is shifting away from the older epidemics such as in north‐eastern homosexual communit

ISSN:0277-6715    

DOI:10.1002/sim.4780080104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractShort‐term projections of AIDS incidence are critical for assessing future health care needs. This paper focuses on the method of back‐calculation for obtaining short‐term projections. The approach consists of back‐calculating from AIDS incidence data through use of the incubation period distribution to obtain estimates of the numbers previously infected. The numbers previously infected are then projected forward to obtain short‐term projections. An approach is suggested for accounting for new infections in short‐term projections of AIDS incidence. Back‐calculation requires accurate AIDS incidence data. A method which is computationally easy to implement is proposed for estimating the distribution of the delays in reporting AIDS cases. It was found that the reporting delay distribution in the United States varies by geographic region of diagnosis. Back‐calculation also requires a reliable estimate of the incubation period distribution. Statistical issues associated with estimating the incubation period distribution are considered. The methods are applied to obtain short‐term projections of AIDS incidence in the United States. The projected cumulative AIDS incidence in the U.S. by the end of 1992 was 287,100 under the assumption that there are no new infections after 1 July 1987, and 330,600 under the assumption that the infection rate remains constant. These projections do not account for the new broadened AIDS surveillance definitions or the underreporting of AIDS cases to the Centers fo

ISSN:0277-6715    

DOI:10.1002/sim.4780080105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractChanges over time in the cumulative number of cases of AIDS depend in a complex way on several features of the epidemic, including the distribution of the induction time between infection with the human immunodeficiency virus (HIV) and onset of symptoms of AIDS, heterogeneity in such behaviours as sexual practices, selection of partners, and IV drug use, and changes over time in these behaviours. Consequently, the observed increase in the doubling time in cumulative AIDS incidence from 5 to 13 months, since AIDS was first recognized in 1982, demonstrates neither that the epidemic has begun to ‘run its course’ nor that behavioural changes have had a major impact in reducing incidence. Even in a homogeneous population with known induction distribution, AIDS incidence data currently are of little value in determining the number of persons infected with HIV unless additional information is available about the shape of cumulative incidence curve of HIV infect

ISSN:0277-6715    

DOI:10.1002/sim.4780080106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractStatistical models of the HIV infection epidemic in the U.S. which account for the observed incidence of AIDS cases in the years 1978–1987 are considered. The models assume a known distribution of times from infection to AIDS. The best model estimates that there were approximately 563,000 to 1,110,000 individuals infected in the U.S. in April 1987. These estimates do not take into account underreporting of AIDS cases.The sensitivity of the conclusions to the model's assumptions is ascertained by investigating a variety of parametric models for the infection epidemic, a variety of likely distributions for the time from infection to AIDS, and some plausible alternatives for the history of AIDS cases in the U.S. It is concluded that there is too much uncertainty in the data and the models to be able to give highly accurate predictions of the number of people currently infected in the U.S., however, the results from the best fitting models suggest that there are less than the 1 to 1·5 million infected as estimated by the Centers for Disease Control. A Bayesian scheme is suggested for incorporating the uncertainty in the mode

ISSN:0277-6715    

DOI:10.1002/sim.4780080107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractEpidemic models are developed to evaluate the potential benefits of voluntary confidential testing (VCT) for HIV. The number of tests required to prevent one case (called the economic ratio ER), and the number of cases prevented by the screening programme are calculated. Methods differ from commonly used epidemic models because susceptibles and infecteds are subdivided according to testing status, to permit modelling of the efficacy of knowledge of HIV status in retarding epidemic spread. The methods also allow for subdivision into several homogeneous subpopulations whose members may be attracted in varying degrees to members of other subpopulations. Thus the common assumption of free mixing across subpopulations is relaxed. The following conclusions which refer to a population of 100,000 persons over a period of 5 to 15 years, are robust to wide variations in assumed parameter values and other aspects of modelling:1VCT prevents hundreds or thousands of infections in isolated high risk populations and ER values are typically less than 100, making VCT very attractive economically.2VCT prevents only a few infections in isolated low risk populations with initial prevalence 0‐1 per cent or less, and the ER values are well above 2000. However, in ‘low risk’ populations with 1 per cent initial prevalence, tens or hundreds of infections may be prevented, and ER values fall below 2000 for plausible spread rates, indicating that VCT may be economically feasible in such settings.3In a mixed population of gays, bisexuals and heterosexuals, a VCT programme that aims primarily at the gay/bisexual subpopulations prevents more disease in the gay/bisexual populations, prevents more disease in the heterosexual populations, and requires fewer tests per case prevented than a VCT programme that tests all subpopulations eq

ISSN:0277-6715    

DOI:10.1002/sim.4780080108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper analyses the probability of contracting the AIDS virus in relation to the number of sexual contacts and the number of different partners. It is shown that in the case of a fixed numbernof sexual contacts there is the following ranking from least risk to greatest risk: 1. a monogamous relationship with a non‐infected partner; 2. a monogamous relationship with a randomly selected partner; 3. a relationship with more than one randomly selected partners; 4.nrandomly selected partners; 5. a monogamous relationship with an infected partne

ISSN:0277-6715    

DOI:10.1002/sim.4780080109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractRecent studies have indicated variation in the infectivity β of HIV among heterosexual couples. We represent this heterogeneity by modelling β as a random variable. Using data on the number of contacts and seroconversion of couples, we fit the model by maximum‐likelihood estimation with a beta distribution and a discrete distribution for β. The estimates indicate the heterogeneity is extreme. The limitations of the model and the implications of the results for epidemiologic spread and further research are discu

ISSN:0277-6715    

DOI:10.1002/sim.4780080110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe objective of the computer simulation model described here is to project, for periods up to one or more decades, the annual incidence and prevalence of HIV infection and AIDS in a population with given epidemiological, behavioural and demorgraphic characteristics. In addition, the epidemic's impact on a range of demographic variables is calculated. The epidemiological components of the model use a compartmental approach and they are described with sets of linear differential equations. The demographic framework in which the epidemiological components are integrated, is based on a standard cohort component method of population projection. The simulated population is stratified by age, gender, sexual behaviour, marital status and infection/disease status. The concluding section provides an illustrative application of the model to a Central African population. In this hypothetical simulation covering the period from 1975 to 2000, HIV prevalence in the adult population rises from 0 to 21 per cent. By the end of the projection period mortality is about double the level that would have prevailed in the absence of the epidemic, but, owing to the very high birth rates that prevail in most of Africa, the growth rate of the population remains substantially positive.

ISSN:0277-6715    

DOI:10.1002/sim.4780080111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractIn this paper we propose a stochastic model for the AIDS spread in a homosexual population. The probability generating function (PGF) of the numbers of latent persons, infective persons and AIDS cases is derived. By using the PGF, it is shown that the expected numbers and variances and covariances of these persons satisfy some ordinary differential equations. These equations have been solved numerically to assess effects of various factors on AIDS spread.

ISSN:0277-6715    

DOI:10.1002/sim.4780080112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY