Deconvolution Methods Back Calculating the Incubation Distribution

Another approach to estimating the incubation period distribution uses population AIDS incidence data and estimates of the HIV infection rates in the population (Bacchetti and Moss, 1989 Bacchetti, 1990). The expected cumulative AIDS incidence up to calendar time , A(t), is related to infection rates at calendar times g(s), and the incubation period distribution, by the convolution equation The basic idea is to use data on A(t) and an estimate of (i) to glean information about F. These methods...

Synthesis Of Knowledge Of The Incubation Period Distribution

The main complexities in the analysis and interpretation of epidemiological studies of the incubation period include uncertainty in the dates of infection and the sampling criteria by which individuals are included in the data set. Synthesizing and comparing estimates across studies is important since the estimates are typically based on various methodologies with different underlying assumptions. Reviews of studies of the incubation period distribution have been given by Moss and Bacchetti...

Prevention Efforts

In order to prevent infection from contaminated blood, efforts have been made to reduce HIV prevalence in the population of donors and to screen donated blood for HIV. To increase the sensitivity of the screening procedure, blood is ejected if the first EI A is positive, even if that result is not later confirmed by a second EIA or by WB. Nonetheless, because of the silent interval, there remain rare instances of infection from blood products. Risks of failing to detect blood from infections in...

Duration Of The Preantibody Phase

The interval between first exposure to HIV and the development of detectable antibodies (seroconversion) is called the pre-antibody phase. The duration of the pre-antibody phase has important implications for the scope of the epidemic because individuals could be infectious even though they test seronegative (no detectable antibodies). The duration of the pre-antibody phase is uncertain. The major methodological problem with studies of the pre-antibody phase is that the calendar time of first...

HuPu I HijPuJr923

Equation (9.23) is zero for all i 1,2, , and for yt 0 only when the yi are eigenvectors corresponding to the eigenvalues of the I x matrix of coefficients of yi in (9.23). In fact, the epidemic will grow if the dominant eigenvalue of the matrix ty0y exceeds a, and the basic reproductive ratio of the epidemic can be defined as R0 maximal eigenvalue of ( Xy0y) a. As an illustration, consider a population containing ny 1000 heterosexuals with fi1+ 5 and n2 9000 heterosexuals with fi2 + 1, and...

Homosexual and Bisexual Males

The San Francisco infection curve for homosexual men (Figure 1.5) estimated by Bacchetti (1990) has a doubling time of about 3 months in July 1978, 5 months in January 1979, and 8 months in July 1979. Data from the San Francisco City Clinic Cohort also indicate a doubling time of about 8 months in early 1979 (Winkelstein, Samuel, and Padian, 1987). We shall try to use this information to obtain an indirect estimate of the probability of transmission per partnership, . Winkelstein, Lyman,...

Forecasting Pediatric Aids

In this section, we review some methodological approaches for assessing the scope of the pediatric AIDS epidemic. The incubation period of perinatally transmitted HIV infection is somewhat shorter than for other transmission modes (Auger, Thomas, De Gruttola, 1988). Furthermore, in some settings one has access to nearly exhaustive HIV seroprevalence surveys among newborns. Thus, the preferred methodological approaches for assessing the scope of pediatric AIDS are different than for adult AIDS....

The Role of Selective Mixing

The simple two-compartment models in Sections 9.2 and 9.3 ignore the fact that real populations are not homogeneous. It is usually more realistic to regard populations as consisting of subgroups with various levels of risk behavior and to study the impact of such heterogeneity of risk behavior and of various possible mixing patterns that describe how frequently members of these subpopulations interact to transmit infection. Such subgroups could differ not only in their rates of new partnership...

Hiv Virus And Its Clinical Effects

Until 1970, it was assumed that genetic information was always transcribed from DNA into RNA, but in 1970 it was discovered that certain viruses, called retroviruses, used RNA to carry their genetic information, and, moreover, employed the enzyme reverse transcriptase to transcribe the RNA into DNA in the cells of the infected host (Temin and Mitzutani, 1970 Baltimore, 1970). HIV-1 turns out to be such a retrovirus. After attaching to the host cell wall, HIV-1 releases its RNA together with...

A Closed Twocompartment Model 921 Model Definition and Properties

Suppose a large number of individuals, jV0, are engaging in behaviors that can transmit HIV, and that the chance of transmission per infected partner contacted is J. To be precise, we are assuming that all contacts with a partner are concentrated into an instant and that fi is the probability that a susceptible partner is infected by having a partnership with an infected partner, without regard to the number or type of sexual acts during the partnership. Suppose the average rate of formation of...

Vaccine Trials

Since the discovery that AIDS was caused by a specific retrovirus, HIV, there has been an urgent desire and effort to develop vaccines to prevent further infections. The biology of HIV poses special problems, however Berzofsky, 1991 . First, the envelope protein of HIV is highly variable, not only among strains in different infected individuals but also among strains that evolve within a single infected individual. Thus, it may be difficult to develop a vaccine that will lead to the production...

AIDS Epidemiology A Quantitative Approach

Department of Biostatistics School of Hygiene and Public Health Johns Hopkins University Epidemiology and Biostatistics Program National Cancer Institute New York Oxford OXFORD UNIVERSITY PRESS 1994 Delhi Bombay Calcutta Madras Karachi Kuala Lumpur Singapore Hong Kong Tokyo Copyright 1994 by Oxford University Press, Inc. Published by Oxford University Press, Inc. 200 Madison Avenue, New York, New York 10016 Oxford is a registered trademark of Oxford University Press All rights reserved. No part...

Statistical Issues in Surveillance of AIDS Incidence

AIDS incidence refers to the numbers of newly diagnosed cases per unit time. Before the development of the HIV antibody screening test Chapter 6 , AIDS incidence data were the only available data for tracking the course of the epidemic. However, trends in AIDS incidence do not reflect current trends in the spread of HIV infection because incubation times are long and variable. Nevertheless, because of the difficulty in conducting representative HIV seroprevalence surveys Chapter 3 , AIDS...