Estimation of risk of cancers before occurrence of acquired immunodeficiency syndrome in persons infected with human immunodeficiency virus.

There is methodological debate as to whether cohorts defined by acquired immunodeficiency syndrome (AIDS) diagnosis can be used to estimate risks of cancer in persons with human immunodeficiency virus (HIV) before AIDS. The authors compared risks of non-AIDS-defining cancers before AIDS in persons with HIV using a cohort based on AIDS diagnosis and a second cohort based on HIV diagnosis. National population-based registries of AIDS and HIV diagnoses to August 1999 were matched separately with the National Cancer Registry in Australia. Four analyses were performed. In analysis 1, follow-up was from 5 years before AIDS registration in 8,118 persons with AIDS. Analysis 2 was similar but adjusted expected numbers of cancers for decreased survival. Analysis 3 was based on 7,061 persons registered with HIV, with follow-up from the reported date of diagnosis. Analysis 4 was based on 2,112 AIDS cases previously reported with HIV, with follow-up from 5 years before AIDS diagnosis. In all analyses, follow-up ended at cancer diagnosis, death, 6 months before AIDS, or the end of available cancer data, whichever occurred first. For 10 types of cancer there were at least three cases in any one of the analyses. For these cancers there was no systematic pattern such that one analysis produced consistently higher or lower estimates than the others. These analyses suggest that cancer risk in persons with HIV before AIDS diagnosis may be estimated reliably based on cancer experience 5 years before AIDS.     

Identifying Hidden Sexual Bridging Communities in Chicago

Bridge populations can play a central role in the spread of human immunodeficiency virus (HIV) by providing transmission links between higher and lower prevalence populations. While social network methods are well suited to the study of bridge populations, analyses tend to focus on dyads (i.e., risk between drug and/or sex partners) and ignore bridges between distinct subpopulations. This study takes initial steps toward moving the analysis of sexual network linkages beyond individual and risk group levels to a community level in which Chicago’s 77 community areas are examined as subpopulations for the purpose of identifying potential bridging communities. Of particular interest are “hidden” bridging communities; that is, areas with above-average levels of sexual ties with other areas but whose below-average AIDS prevalence may hide their potential importance for HIV prevention. Data for this analysis came from the first wave of recruiting at the Chicago Sexual Acquisition and Transmission of HIV Cooperative Agreement Program site. Between August 2005 through October 2006, respondent-driven sampling was used to recruit users of heroin, cocaine, or methamphetamine, men who have sex with men regardless of drug use, the sex partners of these two groups, and sex partners of the sex partners. In this cross-sectional study of the sexual transmission of HIV, participants completed a network-focused computer-assisted self-administered interview, which included questions about the geographic locations of sexual contacts with up to six recent partners. Bridging scores for each area were determined using a matrix representing Chicago’s 77 community areas and were assessed using two measures: non-redundant ties and flow betweenness. Bridging measures and acquired immunodeficiency syndrome (AIDS) case prevalence rates were plotted for each community area on charts representing four conditions: below-average bridging and AIDS prevalence, below-average bridging and above-average AIDS prevalence, above-average bridging and AIDS prevalence, and above-average bridging and below-average AIDS prevalence (hidden bridgers). The majority of the 1,068 study participants were male (63%), African American (74%), and very poor, and the median age was 44 years. Most (85%) were sexually active, and 725 provided useable geographic information regarding 1,420 sexual partnerships that involved 57 Chicago community areas. Eight community areas met or came close to meeting the definition of hidden bridgers. Six areas were near the city’s periphery, and all eight areas likely had high inflows or outflows of low-income persons displaced by gentrification. The results suggest that further research on this method is warranted, and we propose a means for public health officials in other cities to duplicate the analysis.     

Identifying Hidden Sexual Bridging Communities in Chicago

Bridge populations can play a central role in the spread of human immunodeficiency virus (HIV) by providing transmission links between higher and lower prevalence populations. While social network methods are well suited to the study of bridge populations, analyses tend to focus on dyads (i.e., risk between drug and/or sex partners) and ignore bridges between distinct subpopulations. This study takes initial steps toward moving the analysis of sexual network linkages beyond individual and risk group levels to a community level in which Chicago’s 77 community areas are examined as subpopulations for the purpose of identifying potential bridging communities. Of particular interest are “hidden” bridging communities; that is, areas with above-average levels of sexual ties with other areas but whose below-average AIDS prevalence may hide their potential importance for HIV prevention. Data for this analysis came from the first wave of recruiting at the Chicago Sexual Acquisition and Transmission of HIV Cooperative Agreement Program site. Between August 2005 through October 2006, respondent-driven sampling was used to recruit users of heroin, cocaine, or methamphetamine, men who have sex with men regardless of drug use, the sex partners of these two groups, and sex partners of the sex partners. In this cross-sectional study of the sexual transmission of HIV, participants completed a network-focused computer-assisted self-administered interview, which included questions about the geographic locations of sexual contacts with up to six recent partners. Bridging scores for each area were determined using a matrix representing Chicago’s 77 community areas and were assessed using two measures: non-redundant ties and flow betweenness. Bridging measures and acquired immunodeficiency syndrome (AIDS) case prevalence rates were plotted for each community area on charts representing four conditions: below-average bridging and AIDS prevalence, below-average bridging and above-average AIDS prevalence, above-average bridging and AIDS prevalence, and above-average bridging and below-average AIDS prevalence (hidden bridgers). The majority of the 1,068 study participants were male (63%), African American (74%), and very poor, and the median age was 44 years. Most (85%) were sexually active, and 725 provided useable geographic information regarding 1,420 sexual partnerships that involved 57 Chicago community areas. Eight community areas met or came close to meeting the definition of hidden bridgers. Six areas were near the city’s periphery, and all eight areas likely had high inflows or outflows of low-income persons displaced by gentrification. The results suggest that further research on this method is warranted, and we propose a means for public health officials in other cities to duplicate the analysis.     

HIV and AIDS surveillance among inmates in Maryland prisons

The prevalence of those with human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS) is higher among inmates of correctional facilities than among the general population. This raises the need to identify inmates living with or at risk of HIV/AIDS and to provide counseling and appropriate survices for HIV treatment and prevention. The Maryland Division of Corrections (DOC) offers voluntary testing to all inmates on entry and tests inmates when clinically indicated. We reviewed all 1998 HIV antibody tests and confirmed AIDS cases in the Maryland DOC. Inmate demographics, testing acceptance, rates of seropositivity, and AIDS cases and comparisons based on gender, racelethnicity, and age were examined. Comparisons were also made to HIV testing and AIDS cases from the nonincarcerated Maryland population. Trends in DOC AIDS diagnoses and AIDS-related deaths over time were also examined. Of the inmates, 39% were voluntarily tested for HIV on entry to the Maryland DOC in 1998 (38% of males and 49% of females). Overall, HIV seropositivity was 33% (5% for females and 3% for males). The 888 cumulative AIDS cases diagnosed in the DOC inmate population were concentrated among males (90% vs. 77% statewide), African Americans (91% vs. 75% statevide), and among IDUs (84% vs. 39% statewide). Due to high rates of HIV and AIDS, inmate populations are a crucial audience for HIV/AIDS testing, treatment, and prevention efforts, especially women. Prison-based programs can identify significant numbers of HIV and AIDS cases and bring HIV prevention interventions to a population characterized by frequent high-risk behavior.     

Projections of HIV infections and AIDS cases to the year 2000

After the recognition of AIDS (acquired immunodeficiency syndrome) in the early 1980s, uncertainty about the present and future dimensions of HIV (human immunodeficiency virus) infection led to the development of many models to estimate current and future numbers of HIV infections and AIDS cases. The Global Programme on AIDS (GPA) of the World Health Organization (WHO) has developed an AIDS projection model which relies on available HIV seroprevalence data and on the annual rate of progression from HIV infection to AIDS for use in areas where reporting of AIDS cases is incomplete, and where scant data are available to quantify biological and human behavioural variables. Virtually all models, including the WHO model, have projected large increases in the number of AIDS cases by the early 1990s. Such short-term projections are considered relatively reliable since most of the new AIDS cases will develop in persons already infected with HIV. Longer-term prediction (10 years or longer) is less reliable because HIV prevalence and future trends are determined by many variables, most of which are still not well understood. WHO has now applied the Delphi method to project HIV prevalence from the year 1988 to mid-2000. This method attempts to improve the quality of the judgements and estimates for relatively uncertain issues by the systematic use of knowledgeable "experts". The mean value of the Delphi projections for HIV prevalence in the year 2000 is between 3 and 4 times the 1988 base estimate of 5.1 million; these projections have been used to obtain annual estimates of adult AIDS cases up to the year 2000. Coordinated HIV/AIDS prevention and control programmes are considered by the Delphi participants to be potentially capable of preventing almost half of the new HIV infections that would otherwise occur between 1988 and the year 2000. However, more than half of the approximately 5 million AIDS cases which are projected for the next decade will occur despite the most rigorous and effective HIV/AIDS prevention efforts since these AIDS cases will develop in persons whose HIV infection was acquired prior to 1989. The Delphi projections of HIV infection and AIDS cases derived from the WHO projection model need to be periodically reviewed and modified as additional data become available. These projections should be viewed as the first of many attempts to develop estimates for planning strategies to combat the HIV/AIDS pandemic in the 1990s.     

Desperately seeking targets: the ethics of routine HIV testing in low-income countries

The human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS) pandemic, and responses to it, have exposed clear political, social and economic inequities between and within nations. The most striking manifestations of this inequity is access to AIDS treatment. In affluent nations, antiretroviral treatment is becoming the standard of care for those with AIDS, while the same treatment is currently only available for a privileged few in most resource-poor countries. Patients without sufficient financial and social capital -- i.e., most people with AIDS -- die each day by the thousands. Recent AIDS treatment initiatives such as the UNAIDS and WHO "3 by 5" programme aim to rectify this symptom of global injustice. However, the success of these initiatives depends on the identification of people in need of treatment through a rapid and massive scale-up of HIV testing. In this paper, we briefly explore key ethical challenges raised by the acceleration of HIV testing in resource-poor countries, focusing on the 2004 policy of routine ("opt-out") HIV testing recommended by UNAIDS and WHO. We suggest that in settings marked by poverty, weak health-care and civil society infrastructures, gender inequalities, and persistent stigmatization of people with HIV/AIDS, opt-out HIV-testing policies may become disconnected from the human rights ideals that first motivated calls for universal access to AIDS treatment. We leave open the ethical question of whether opt-out policies should be implemented, but we recommend that whenever routine HIV-testing policies are introduced in resource-poor countries, that their effect on individuals and communities should be the subject of empirical research, human-rights monitoring and ethical scrutiny.     

Retention of women enrolled in a prospective study of human immunodeficiency virus infection: impact of race, unstable housing, and use of human immunodeficiency virus therapy.

Even though women and people of color represent an increasing proportion of US acquired immunodeficiency syndrome (AIDS) cases, few research studies include adequate representation of these populations. Here the authors describe recruitment and retention of a diverse group of human immunodeficiency virus (HIV)-infected and at risk HIV-uninfected women in a prospective study operating in six sites across the United States. Methods used to minimize loss to follow-up in this cohort are also described. For the first 10 study visits that occurred during a 5-year period between 1994 and 1999, the retention rate of participants was approximately 82%. In adjusted Cox analysis, factors associated with retention among all women were older age, African-American race, stable housing, HIV-infected serostatus, past experience in studies of HIV/AIDS, and site of enrollment. In an adjusted Cox analysis of HIV-infected women, African-American race, past experience in studies of HIV/AIDS, site of enrollment, and reported use of combination or highly active antiretroviral HIV therapy at the last visit were significantly associated with retention. In adjusted Cox analysis of HIV-uninfected study participants, only the site of enrollment was significantly associated with study retention. These results show that women with and at risk for HIV infection, especially African-American women, can be successfully recruited and retained in prospective studies.     

A comparison of ad hoc methods to account for non-cancer AIDS and deaths as competing risks when estimating the effect of HAART on incident cancer AIDS among HIV-infected men

ObjectiveTo compare three ad hoc methods to estimate the marginal hazard of incident cancer acquired immune deficiency syndrome (AIDS) in a highly active antiretroviral therapy (1996–2006) relative to a monotherapy/combination therapy (1990–1996) calendar period, accounting for other AIDS events and deaths as competing risks.Study Design and SettingAmong 1,911 human immunodeficiency virus (HIV)-positive men from the Multicenter AIDS Cohort Study, 228 developed cancer AIDS and 745 developed competing risks in 14,202 person-years from 1990 to 2006. Method 1 censored competing risks at the time they occurred, method 2 excluded competing risks, and method 3 censored competing risks at the date of analysis.ResultsThe age, race, and infection duration adjusted hazard ratios (HRs) for cancer AIDS were similar for all methods (HR ≈ 0.15). We estimated bias and confidence interval coverage of each method with Monte Carlo simulation. On average, across 24 scenarios, method 1 produced less-biased estimates than methods 2 or 3.ConclusionsWhen competing risks are independent of the event of interest, only method 1 produced unbiased estimates of the marginal HR, although independence cannot be verified from the data. When competing risks are dependent, method 1 generally produced the least-biased estimates of the marginal HR for the scenarios explored; however, alternative methods may be preferred.     

An age- and sex-structured HIV epidemiological model: features and applications.

An important challenge in modelling the human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) epidemic is to use the increasing quantity of disease surveillance data to validate estimates and forecasts. Presented is a novel model for forecasting HIV incidence by age and sex and among sentinel groups for which data are available. This approach permits a closer relationship between forecasting and surveillance activities, and more accurate estimates validated to data. As inputs the model uses an estimate of the HIV prevalence, country demographic data, and a profile of the sexual risk of HIV infection by age, to project HIV incidence, prevalence, number of AIDS cases and population. The following examples of the use of the model are given: forecasting HIV incidence in East Africa, by age, sex, and among pregnant women; 3-5-year forecasts of HIV incidence; modelling mixed risk behaviour HIV epidemics in South-east Asia; demographic indicators; and targeting a preventive vaccine by age group.     

Computing back-calculation estimates of aids epidemic

The method of back-calculation estimates the number of HIV infections from AIDS incidence data and projects future AIDS incidence. We explore a conditional likelihood approach for computing estimates of the number of HIV infections and the parameters in the epidemic density. This method is asymptotically equivalent to the usual likelihood method. The asymptotic normal distribution of the estimates facilitates the computation of confidence intervals. We compute standard deviations for the estimates of HIV incidence and project AIDS incidence from the underlying multinomial distributions. We illustrate the methods with applications to AIDS data in the United States.     

Increases in HIV diagnoses--29 States, 1999-2002

Since the advent of highly active antiretroviral therapy (HAART) in 1996, progression from receiving diagnosis of human immunodeficiency virus (HIV) infection to having acquired immunodeficiency syndrome (AIDS) has slowed substantially, making HIV-transmission patterns less predictable through AIDS surveillance alone. Consequently, CDC has recommended that states report diagnoses of HIV infections in addition to cases of AIDS. Recent estimates of HIV diagnoses suggested a leveling of the downward trend in HIV infections nationally and increases in HIV infections among certain populations. Reports of syphilis outbreaks and increased unprotected sex raised concerns regarding increases in HIV transmission among men who have sex with men (MSM). In response to these developments, CDC analyzed trends in HIV diagnoses in 29 states that conducted name-based HIV/AIDS surveillance during 1999-2002. This report summarizes the results of that study, which indicated that HIV diagnoses increased among men, particularly MSM, and also among non-Hispanic whites and Hispanics. The findings emphasize the need for new prevention strategies to reverse potential increases in HIV transmission among these populations.     

Uncertainty in estimates of HIV prevalence derived by backcalculation.

The incidence of consistently defined acquired immunodeficiency syndrome (AIDS) among adults in the United States was used to "backcalculate" the prevalence of human immunodeficiency virus (HIV) as of January 1, 1985, and July 1, 1987. The sensitivity of estimates to random and systematic sources of uncertainty was assessed. Using a "standard" incubation distribution with a 10-year median time-to-AIDS, we estimated that 544,000 persons were infected as of January 1, 1985, and that 992,000 persons were infected as of July 1, 1987. Variation from model selection and fitting was only 2% and 5%, respectively. Perturbations of the AIDS incidence counts to reflect plausible reporting biases reduced prevalence estimates by as much as 9.6% and 16.0%, respectively. Uncertainty about the incubation distribution had an even greater impact. A "plausible range" of prevalence estimates was calculated using alternative "Fast" and "Slow" incubation distributions. The plausible range varied from 415,000 to 760,000 persons in 1985 and from 737,000 to 1.4 million persons in July 1987. Inclusion of AIDS incidence counts beyond mid-1987 can lead to serious underestimates of prevalence, because use of zidovudine and other therapies beginning in mid-1987 has lengthened the incubation distribution in many severely immunodepressed persons without AIDS.     

A method for classification of HIV exposure category for women without HIV risk information.

An increasing number of cases of human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS) among women is reported to state and territorial health departments without exposure risk information (i.e., no documented exposure to HIV through any of the recognized routes of HIV transmission). Because surveillance data are used to plan prevention and other services for HIV-infected persons, developing methods to accurately estimate exposure risk for HIV and AIDS cases initially reported without risk information and assisting states to analyze and interpret trends in the HIV epidemic by exposure risk category is important. In this report, a classification model using discriminant function analysis is described. The purpose of the classification model is to develop a proportionate distribution of exposure risk category for cases among women reported without risk information. The distribution was estimated based on behavioral and demographic data obtained from interviews with HIV-infected women; the interviews were conducted in 12 states during 1993-1996. Variables used in the analysis were alcohol abuse, noninjection-drug use, and crack use; year of HIV/AIDS diagnosis; age; employment; and region. As a result of the classification procedure, nearly all cases among women with no reported risk were classified into an exposure risk category: 81%, heterosexual contact; and 16%, injection-drug use. These proportions are higher than the current redistribution fractions (calculated from risk reclassification patterns and weighted by demographic characteristics) and reflect the increasing proportion of cases among women attributable to heterosexual contact with an infected partner. This report provides one method that could be applied to HIV surveillance data at the national level to estimate the proportion of cases in exposure risk categories. However, because the study in this report is limited in sample size and geographic representativeness, other models are also needed for adjusting risk exposure data at the national, state, and local levels.     

Racial/ethnic disparities in diagnoses of HIV/AIDS--33 states, 2001-2005

During 2001-2004, blacks accounted for 51% of newly diagnosed human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) infections in the United States. This report updates HIV/AIDS diagnoses during 2001-2005 among black adults and adolescents and other racial/ethnic populations reported to CDC through June 2006 by 33 states that had used confidential, name-based reporting of HIV and AIDS cases since at least 2001. Of the estimated 184,991 adult and adolescent HIV infections diagnosed during 2001-2005, more (51%) occurred among blacks than among all other racial/ethnic populations combined. Most (62%) new HIV/AIDS diagnoses were among persons aged 25-44 years; in this age group, blacks accounted for 48% of new HIV/AIDS diagnoses. New interventions and mobilization of the broader community are needed to reduce the disproportionate impact of HIV/AIDS on blacks in the United States.     

Self-reported HIV and AIDS experience, practices, and knowledge of Pennsylvania family physicians.

BACKGROUND: Patients with disease caused by the human immunodeficiency virus (HIV), while still more commonly treated in urban settings, are being seen in nonurban areas in numbers rapidly outstripping the local availability of specialists with expertise in HIV or acquired immunodeficiency syndrome (AIDS). METHODS: A questionnaire designed to measure self-assessed experience, practices, and knowledge regarding basic aspects of HIV was mailed in 1989 to the 2177 members of the Pennsylvania Academy of Family Physicians. RESULTS: The response rate was 72 percent. Approximately 95 percent of physicians surveyed had been asked questions by patients about AIDS, 30 percent had a patient with a confirmed positive blood test, and 27 percent had a patient with symptomatic HIV disease in their practice. CONCLUSIONS: Although most family physicians indicated that they were comfortable in recognizing persons at risk, counseling, and using tests to diagnose HIV and AIDS, more than one-half reported practice patterns at variance with published guidelines. Respondents were most uncomfortable with their knowledge and skills regarding legal issues, state and community resources, and caring for patients with AIDS. Continuing medical education courses at local hospitals and written materials were the two methods of AIDS education most likely to be used by respondents.     

Multinomial analysis of smoothed HIV back-calculation models incorporating uncertainty in the AIDS incidence.

Back-calculation models, developed to reconstruct the past trend of human immunodeficiency virus (HIV) and to project future acquired immunodeficiency syndrome incidence (AIDS), are usually and unrealistically based on the assumption that the observed AIDS counts are independently distributed according to a Poisson process. In contrast, we argue that a multinomial framework is more suitable to this situation, leading to a natural covariance structure. The ill-conditioned nature of the problem is solved by modelling the HIV parameters according to a cubic spline function to reduce the dimensionality of the parameter space and obtain smoother parameter estimates. We applied a regression spline technique which yields to a computationally stable basis incorporating the incubation period in the new design matrix. We directly incorporate the reporting delay distribution in the AIDS incidence data, leading to a more complex formulation of the variance and covariance model that is adapted to the iteratively reweighted least square (IRLS) algorithm. In this case we obtain more accurate estimates of the standard error of the HIV incidence, especially in the most recent time. Our model, which uses a cubic spline reparameterization based on a multinomial probability distribution, is applied to the AIDS epidemic data in Italy. Copyright John Wiley & Sons, Ltd.     

Backcalculation of the number with human immunodeficiency virus infection in the United States

The method of backcalculation was applied to national surveillance data on the acquired immunodeficiency syndrome (AIDS) in order to estimate the cumulative number of adults with human immunodeficiency virus type 1 (HIV-1) infection as of January 1, 1985 and July 1, 1987. A "plausible range" of estimates was constructed which reflected both uncertainty about the AIDS incubation distribution and random variation from selection and fitting of flexible models of the HIV-1 infection curve. The authors estimated that, as of 1985, 411,000 to 756,000 persons were infected. The infected population included 266,000 to 492,000 homosexual men, 69,000 to 136,000 intravenous drug users, 24,000 to 49,000 homosexual intravenous drug users, and 11,000 to 26,000 persons infected through heterosexual contact. The estimated prevalence of infection among persons aged 15-55 years was 0.31% in whites, 0.78% in Hispanics, and 0.81% in blacks. An estimated 32,000 to 66,000 women were infected. Compared with white women aged 15-55 years, the prevalence of infection was 5.3-fold higher in Hispanic women and 10.2-fold higher in black women. Plausible estimates for the total number infected by July 1987 ranged from 707,000 to 1,376,000, with the most likely estimate equal to 992,000. Backcalculation provides an assessment of the magnitude of the HIV-1 epidemic that is independent of estimates based on prevalence surveys in special populations. The estimates obtained from both methods are consistent and emphasize the need for vigorous programs to prevent the spread of HIV-1, especially in minority communities.     

Lack of HIV Seropositivity Among a Group of Rural Probationers: Explanatory Factors

CONTEXT: Human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) in rural America has been described as an epidemic, and the HIV prevalence rate among criminal justice populations is higher than the general population. Thus, criminally involved populations in Southern rural areas are at elevated risk for contracting HIV because of drug and sexual practices; however, little is known about HIV/AIDS in the fastest growing criminal justice population-probationers. PURPOSE: To examine possible explanations for the lack of HIV seropositivity found in a purposive sample of rural probationers. METHODS: Data were examined from 800 felony probationers from 30 counties in Kentucky's Appalachian region. Measures included HIV prevalence within the 30 counties, migration patterns, HIV knowledge, substance use, and sexual risk behaviors. FINDINGS: These probationers had a high level of HIV knowledge, reported minimal injection drug use, practiced serial monogamy, and reported minimal engagement in transactional sex. However, these probationers also reported negligible condom use, and injection drug users shared needles and works. CONCLUSION: Findings suggest the importance of developing programs targeting safe sex practices in rural areas.     

Public health surveillance of AIDS and HIV infections

The general methods used for public health surveillance of acquired immunodeficiency syndrome (AIDS) cases and of human immunodeficiency virus (HIV) infections are no different from those used for other diseases and infections. However, the methods used must be adapted to the unique epidemiology, wide variation in prevalences, and the very long incubation period of HIV infections. In addition, the severity of AIDS and the extreme social and personal implications of identifying HIV-infected persons make surveillance of AIDS cases and HIV infections much more difficult and place paramount importance on issues such as anonymity and confidentiality. Information on the occurrence of AIDS cases is essential for planning and developing the clinical and laboratory facilities needed for treatment and care of patients with the disease. However, surveillance of AIDS cases is of limited value for assessing the magnitude and future trends of the pandemic because the number of such cases detected, diagnosed, and reported reflect HIV infections that were acquired many years previously. In addition, there are significant problems associated with the accuracy, completeness, and timeliness of most AIDS case-reporting systems. Routine HIV surveillance systems are being developed worldwide. Such systems must be adapted to the prevailing epidemiological situation; and the sampling methods used in populations where the prevalence of infection is very low must necessarily differ from those where it is moderate to high. Large-scale population serosurveys are very costly, and the results from such surveys may also be of limited accuracy because of serious problems of selection and participation bias. Furthermore, they may become outdated rapidly in areas where a high incidence of HIV infection occurs.(ABSTRACT TRUNCATED AT 250 WORDS)     

The prevalent cohort study and the acquired immunodeficiency syndrome

The acquired immunodeficiency syndrome (AIDS) is caused by a retrovirus, the human immunodeficiency virus (HIV). A rapid and convenient method to identify additional cofactors or risk modifiers and markers of disease progression is to study a cohort prevalent with HIV antibody. However, because the time of viral infection is usually unknown in the cohort, there are several potential sources of bias. Three sources of bias in a prevalent cohort study are identified assuming a proportional hazards model: onset confounding, differential length-biased sampling, and frailty selection. A number of problems in the interpretation of results on markers from a prevalent cohort also are considered. It is concluded that risk estimates derived from a prevalent cohort are not directly comparable to risk estimates derived from an incident cohort.