Estimation of HIV infection and incubation via state space models

By using the state space model (Kalman filter model) of the HIV epidemic, in this paper we have developed a general Bayesian procedure to estimate simultaneously the HIV infection distribution, the HIV incubation distribution, the numbers of susceptible people, infective people and AIDS cases. The basic approach is to use the Gibbs sampling method combined with the weighted bootstrap method. We have applied this method to the San Francisco AIDS incidence data from January 1981 to December 1992. The results show clearly that both the probability density function of the HIV infection and the probability density function of the HIV incubation are curves with two peaks. The results of the HIV infection distribution are clearly consistent with the finding by Tan et al. [W.Y. Tan, S.C. Tang, S.R. Lee, Estimation of HIV seroconversion and effects of age in San Francisco homosexual populations, J. Appl. Stat. 25 (1998) 85]. The results of HIV incubation distribution seem to confirm the staged model used by Satten and Longini [G. Satten, I. Longini, Markov chain with measurement error: estimating the 'true' course of marker of the progression of human immunodeficiency virus disease, Appl. Stat. 45 (1996) 275].     

Accommodating change due to treatment in the method of back projection for estimating HIV infection incidence

This note shows how the method of back projection, which is being widely applied to predict the incidence of HIV infection, can be extended to incorporate distributional changes due to a treatment effect, such as zidovudine (commonly known as AZT). By way of example we consider one of the approaches to back projection and apply the method to some Australian data.     

Changes in sexual behaviour and the fall in incidence of HIV infection among homosexual men.

To investigate the epidemiology and normal course of infection with HIV the prevalence and incidence of the infection were studied among two cohorts of homosexual men in Amsterdam in 1980-7. The cumulative incidence of infection increased from a weighted 2.2% in 1980 to 39.0% in 1987. The estimated yearly incidence of HIV was 3.0% in 1981, rose to 8.8% in 1984, and fell gradually to 0% in 1987. During the study the sexual behaviour of the cohorts was examined. The number of men with whom anopenetrative intercourse was practised fell from a mean of 10.6 to 1.4 for those positive for HIV antibody, whereas the number with whom anoreceptive intercourse was practised fell from a mean of 3.7 to 0.5 for those negative for the antibody. In addition, there was a reduction in the number of cases of hepatitis B and syphilis among men in general. The decline in infection with HIV was assumed to be linked to changes in sexual behaviour. Such changes practised early in the course of the epidemic probably had a strong effect on the number of cases of AIDS among homosexual men in Amsterdam.     

Estimation of the Distribution of Infection Times Using Longitudinal Serological Markers of HIV: Implications for the Estimation of HIV Incidence

Summary In the last decade, interest has been focused on human immunodeficiency virus (HIV) antibody assays and testing strategies that could distinguish recent infections from established infection in a single serum sample. Incidence estimates are obtained by using the relationship between prevalence, incidence, and duration of recent infection (window period). However, recent works demonstrated limitations of this approach due to the use of an estimated mean “window period.” We propose an alternative approach that consists in estimating the distribution of infection times based on serological marker values at the moment when the infection is first discovered. We propose a model based on the repeated measurements of virological markers of seroconversion for the marker trajectory. The parameters of the model are estimated using data from a cohort of HIV‐infected patients enrolled during primary infection. This model can be used for estimating the distribution of infection times for newly HIV diagnosed subjects reported in a HIV surveillance system. An approach is proposed for estimating HIV incidence from these results.     

Estimation of the Timing of Perinatal Transmission of HIV

Knowledge of the timing of perinatal transmission of HIV would be valuable for the determination and evaluation of preventive treatments and would shed light on the mechanism of transmission. Estimation of the distribution of the time of perinatal transmission is difficult, however, because tests of infection status can only be undertaken after birth. DNA and RNA polymerase chain reaction (PCR) assays and HIV culture have been the most commonly used diagnostic tests for perinatal HIV infection. Such tests have high sensitivity and specificity, except when they are given shortly after infection. In this paper we use the time-dependent sensitivity of these diagnostic tests to make nonparametric and semiparametric inferences about the distribution of the time of perinatal HIV transmission as well as the cumulative probability of perinatal transmission. The methods are illustrated with data from a clinical trial conducted by the AIDS Clinical Trials group.     

Determination of the spread of HIV from the AIDS incidence history

The relation between the incidence of HIV in the general population, the number of AIDS cases, and the incubation period for the disease is examined. The number of AIDS cases can be expressed in terms of a convolution integral over the incubation period distribution and the temporal history of HIV incidence. In order to determine the level of HIV incidence it is necessary to invert the convolution. In this manner, it is possible to determine the spread of HIV up to the present time from knowledge of the AIDS incidence history and the incubation period. We describe the inversion of the convolution in terms of a Laplace transform technique that is applicable for any given incubation period distribution. Substantial simplifications in the technique are found in the case of an Erlang distribution for the probability density. The spread of HIV infections in the United States is charted through 1988 using AIDS incidence data that are corrected for both the revised AIDS case definition and reporting time delays. The results are consistent with current estimates of the HIV incidence in the United States and show no evidence of saturation in the rate of new infections. Indeed, the rate of new infections still appears to be climbing as of that date. While the technique is unable to predict the future course of the epidemic, it may provide a useful benchmark for comparison with mathematical models of the epidemic. The techniques are conceptually applicable to diseases other than AIDS.     

HIV infection in the penitentiaries of Ukraine

In connection with a sharp increase of the number of HIV-infected persons in the Ukraine the natural growth of the number of such persons in penitentiary institutions was registered, starting from 1995 (455 persons in 1995, 2,937 persons in 1996, 2,779 persons in 1997 and 173 persons during 5 months of 1998). 83% of HIV infection persons were drug addicts introducing drugs intravenously. In 1997 the strategy of decreasing the risk of infection in penitentiary institutions was worked out in collaboration with UNAIDS experts: repressive and isolation measures were replaced with measures aimed at the "decrease of harm". Special attention is given to circumstances aggravating the epidemic situation in HIV infection, and particularly at the sharp growth of morbidity in tuberculosis and syphilis (10.6 and 10.3 times respectively in 1997 in comparison with 1993). In addition, in 1997 the number of person having drug addiction was noted to increase 2.3 times in comparison with 1993. The necessity of taking constant information and educational measures aimed at decreasing the risk of the spread of HIV infection is emphasized.     

HIV infection and the meaning of condoms

Present day meanings associated with condom use among drug-using women and their long term sexual partners include: loss of male protection; violations of constructions of intimacy, fidelity, conjugal bonding, and female identity; illness; and death. Efforts to change condom use patterns must be based on increased vocational, educational, and social opportunities for women. HIV prevention efforts might profit from the design of safer sex interventions informed by the above meanings; intensified mass media campaigns; and a re-contextualization of attitudes, behaviors, and beliefs.     

Leishmania and the pathogenesis of HIV infection

Acquired immunodeficiency syndrome (AIDS) and leishmaniasis overlap in several parts of the world, and microorganisms responsible for these human diseases infect and replicate within the macrophage. Therefore, the opportunity that the pathogenesis of the human immunodeficiency virus (HIV) and Leishmania infections could be modulated within dually infected individual is optimized. The most prominent clinical feature of AIDS is the development of debilitating secondary infections induced by several opportunistic microorganisms, including protozoa. Michel Tremblay, Martin Olivier and Richard Bernier here focus on the recently reported information on the putative cofactor role that the intracellular pathogen of the genus Leishmania may play in the pathogenesis of HIV infection.