Prevalence, incidence, and progression of human immunodeficiency virus infection in homosexual and bisexual men in hepatitis B vaccine trials, 1978-1988

Molecular Epidemiology and Transmission Dynamics of the HIV-1 Epidemic in Ethiopia: Epidemic Decline Coincided With Behavioral Interventions Before ART Scale-Up

Background

Ethiopia is one of the sub-Saharan countries hit hard by the HIV epidemic. Previous studies have shown that subtype C dominates the Ethiopian HIV-1 epidemic, but the evolutionary and temporal dynamics of HIV-1 in Ethiopia have not been closely scrutinized. Understanding the evolutionary and epidemiological pattern of HIV is vital to monitor the spread, evaluate and implement HIV prevention strategies.

Methods

We analyzed 1,276 Ethiopian HIV-1 subtype C polymerase (pol sequences), including 144 newly generated sequences, collected from different parts of the country from 1986 to 2017. We employed state-of-art maximum likelihood and Bayesian phylodynamic analyses to comprehensively describe the evolutionary dynamics of the HIV-1 epidemic in Ethiopia. We used Bayesian phylodynamic models to estimate the dynamics of the effective population size (Ne) and reproductive numbers (Re) through time for the HIV epidemic in Ethiopia.

Results

Our analysis revealed that the Ethiopian HIV-1 epidemic originated from two independent introductions at the beginning of the 1970s and 1980s from eastern and southern African countries, respectively, followed by epidemic growth reaching its maximum in the early 1990s. We identified three large clusters with a majority of Ethiopian sequences. Phylodynamic analyses revealed that all three clusters were characterized by high transmission rates during the early epidemic, followed by a decline in HIV-1 transmissions after 1990. Re was high (4–6) during the earlier time of the epidemic but dropped significantly and remained low (Re < 1) after the mid-1990. Similarly, with an expected shift in time, the effective population size (Ne) steadily increased until the beginning of 2000, followed by a decline and stabilization until recent years. The phylodynamic analyses corroborated the modeled UNAIDS incidence and prevalence estimates.

Conclusion

The rapid decline in the HIV epidemic took place a decade before introducing antiretroviral therapy in Ethiopia and coincided with early behavioral, preventive, and awareness interventions implemented in the country. Our findings highlight the importance of behavioral interventions and antiretroviral therapy scale-up to halt and maintain HIV transmissions at low levels (Re < 1). The phylodynamic analyses provide epidemiological insights not directly available using standard surveillance and may inform the adjustment of public health strategies in HIV prevention in Ethiopia.

Older age at infection and nulliparity are associated with long-term non-progression in female sex workers infected with non-subtype B HIV-1

Studies have reported on HIV-infected, antiretroviral therapy (ART)-naïve individuals who show minimal disease progression despite prolonged infection. The characteristics of these long-term non-progressors (LTNPs) are not well-characterized in populations predominantly infected with non-subtype B HIV-1. Female sex workers in Mombasa, Kenya who acquired HIV-1 were studied to ascertain immunologic disease progression. Long-term non-progression was defined as an ART-naïve duration of infection ≥7 years and a majority of CD4+ cell counts ≥600 cells/µl with a non-declining CD4+ trend. Correlates of long-term non-progression were determined using multivariable logistic regression. Between February 1993 and March 2014, 332 women acquired HIV-1. Of these, 77 (23%) had ≥7 years of follow-up and 13 (17%) were categorized as LTNPs. Factors associated with long-term non-progression included age >30 years at infection (aOR = 9.41, 95% CI: 1.48–59.86, P = 0.005) and nulliparity (aOR = 20.19, 95% CI: 1.36–299.90, P = 0.03). Each log10 copies/ml increase in viral load (VL) set point was associated with a lower likelihood of being a LTNP (aOR = 0.31, 95% CI: 0.12–0.79, P = 0.01). These findings suggest that age and parity may influence the likelihood of long-term non-progression through mechanisms that are not mediated by the effects of these variables on VL. Future studies should seek to determine whether the associations presented are reproducible.

HIV burden in men who have sex with men: a prospective cohort study 2007-2012

We conducted a prospective cohort study among HIV-negative MSM aged 18 years or older between 2007 and 2012 in Beijing, China to measure the rates of incident HIV and identify risk factors for infection. Among 5,800 participants evaluated at enrollment, we identified 486 prevalent cases of HIV (8.4%). Among the 3,625 enrollees who were HIV-negative at enrollment and completed at least one follow-up interview, we identified 440 incident cases of HIV in the follow up period: this constituted an HIV incidence rate of 7.1 per 100 person-years (95% CI: 6.4–7.7). Early treatment of syphilis may have significantly reduced risk of HIV infection (RR: 1.45, 95% CI: 1.11–1.93), while MSM presenting perfect compliance in the cohort did not show reduction in HIV infection. Our study suggested that HIV incidence has been remained high in this sample of Chinese MSM during the intensive preventive intervention, suggesting that we need to find new strategies to prevent HIV infection in this population.

Trends in HIV prevalence and HIV testing among young MSM: five United States cities, 1994-2011

We examined trends in cross-sectional HIV prevalence (a surrogate for incidence) and past 12 month testing behavior among young men who have sex with men (MSM). The Young Men's Survey and the National HIV Behavioral Surveillance System conducted interviews and HIV testing among MSM recruited by venue-based sampling during 1994-2011. Using data from five cities, we determined whether interview year was associated with HIV prevalence and recent testing for MSM ages 18-22 and 23-29 years, after adjusting for city, race/ethnicity, and education. Multivariable analysis demonstrated an overall increase in prevalence among MSM ages 23-29 years, driven by an increase in Baltimore. There was no change in HIV prevalence among MSM ages 18-22 years overall, although prevalence increased in Baltimore. HIV testing increased significantly for both age groups. Gains in HIV testing are encouraging, but increasing prevalence among young MSM in Baltimore suggests increasing incidence and the need for additional efforts for this population.

The syndemic of AIDS and STDS among MSM

The spread of HIV and other STDs among men who have sex with men (MSM) has been labeled a syndemic because in this population a number of different and interrelated health problems have come together and interact with one another. The various elements of the syndemic have an additive effect, each one intensifying the others. These factors include the number of infectious diseases endemic in this population, the high rate of substance abuse problems and psychological disorders, and the significant percentage of MSM who have experienced childhood sexual abuse and other adverse events. While MSM are disproportionately affected by HIV, syphilis, and other STDs, health activists from the gay community have systematically resisted the application of the full range of public health strategies traditionally used to prevent their spread. In the more than three decades since the beginning of the HIV/AIDS epidemic, there have been substantial advances in testing and treatment, yet the infection rate among MSM, and particularly young MSM, remains high, even as it has been dropping among other risk groups. This paper deals with the history of the syndemic, the failure of various risk reduction strategies, and treatment as prevention.

Disproportionate impact of combination antiretroviral therapy on AIDS incidence in Australia: results from a modified back-projection model

The objective of the current study is to describe the impact of Combination antiretroviral therapy (cART) on trends in AIDS incidence over time for selected population groups in Australia, specifically, men who have sex with men (MSM) and injecting drug users (IDUs). A modified back-projection modeling technique was used to predict the number of AIDS diagnoses without cART based on Australia's HIV/AIDS surveillance system database. Modelled estimates indicate that since 1996, the effective cART has reduced overall AIDS cases by ~70 and ~10% among MSM and IDUs respectively. The predicted reduction in AIDS cases among IDUs aged less than 40 years was 36% while there was no reduction predicted for those aged 40 years or older. The impact of cART on AIDS diagnoses has been modest among IDUs. Late presentation, poor access to health services and barriers to uptake of cART may account for the divergence between these population groups.

Prevalence of HIV infection and prior HIV testing among young men who have sex with men. The Baltimore young men's survey

Data are presented from the Baltimore Young Men's Survey, a cross-sectional, venue-based sample survey of risks associated with HIV and report of a prior HIV test, conducted between 1996 and 2000, and enrolling 843 young men who have sex with men (MSM) aged 15-29 years. HIV prevalence was 12.1% overall and racial disparities in HIV prevalence were pronounced (range, 2.9% among non-Hispanic whites to 27.1% among non-Hispanic blacks). Risks independently associated with being HIV-positive were: being between 26 and 29 years of age, being non-Hispanic black or of other/mixed race, having had 20 or more lifetime male sex partners, having been diagnosed with a sexually transmitted disease (STD), and not being currently enrolled in school. The majority of participants (78.9%) reported a prior HIV test. In multivariate analysis, being older, having had five or more lifetime male sex partners, having had anal intercourse with males, reporting an STD diagnosis, and reporting recent unprotected anal sex were associated with report of a prior HIV test. Prevention efforts must address high HIV prevalence among young non-Hispanic black MSM and must make testing and effective counseling for young MSM readily available.

Behavioral mechanisms in HIV epidemiology and prevention: past, present, and future roles

In the 1980s, behavioral variations across geographically and socially defined populations were the central focus of AIDS research, and behavior change was seen as the primary means of controlling HIV epidemics. Today, biological mechanisms--especially other sexually transmitted infections, antiretroviral therapy, and male circumcision--predominate in HIV epidemiology and prevention. We describe several reasons for this shift in emphasis. Although the shift is understandable, we argue for a sustained focus on behavioral mechanisms in HIV research in order to realize the theoretical promise of interventions targeting the biological aspects of HIV risk. We also provide evidence to suggest that large reductions in HIV prevalence may be accomplished by small changes in behavior. Moreover, we contend that behavioral mechanisms will find their proper place in HIV epidemiology and prevention only when investigators adopt a conceptual model that treats prevalence as a determinant as well as an outcome of behavior and that explicitly recognizes the dynamic interdependence between behavior and other epidemiological and demographic parameters.

[Cohort studies and their contribution to the study of HIV infection: main characteristics and limitations]

In this paper, we provide a definition of cohort studies and reviews the main types of cohort studies used in the context of HIV infection. We discuss how the main sources of selection biases in cohort studies are those derived from the lack of observation of the event that determines the origin and/or of the event of interest due to losses to follow-up or development of a competing event, and how this bias must be appropriately taken into account following specific epidemiological methods. Although cohort studies play an essential role in the study of HIV infection, they are logistically complex and require considerable resources. Therefore, strategic planning on the quality and quantity of the information collected must always be accompanied by a resource allocation plan.

Racial Disparities in HIV Incidence Among Young Men Who Have Sex With Men

Recent reports have demonstrated racial disparities in the prevalence of HIV infection among men who have sex with men (MSM). The objectives of this study are to investigate whether racial disparities exist in HIV incidence among young MSM in Baltimore, MD and to examine potential explanations for differences. Data were collected by the Baltimore Young Men's Survey, a cross-sectional venue-based survey (1996 to 2000) enrolling MSM aged 15 to 29 years. HIV incidence was ascertained using the serologic testing algorithm for recent HIV seroconversion. HIV incidence was 4.2% per year (95% confidence interval [CI]: 1.2 to 10.5) among 843 participants. There were substantial racial differences in HIV incidence, ranging from 0 among Hispanics to 11.0% per year (95% CI: 5.5 to 19.7) among non-Hispanic blacks. In multivariate analysis, among MSM at risk for HIV acquisition, race was not associated with unprotected anal intercourse. Independent risks included having more than 4 recent male sexual partners (adjusted odds ratio [AOR] = 1.6, 95% CI: 1.0 to 2.4) and being under the influence of drugs while having sex (AOR = 1.6, 95% CI: 1.1 to 2.3). Non-Hispanic blacks were no more likely than non-Hispanic whites to report these risk behaviors. Possible alternative explanations for the observed racial disparities in HIV incidence and implications for prevention are explored.

The interplay between socio-demographic variables, nutritional and immune status of HIV-positive/AIDS patients

This study examined the association between socio-demographic factors (educational level and employment status) and the nutritional and immune status of 35 HIV-positive/AIDS patients at baseline. Assessment of selected macro-and micronutrient dietary intake was done using a validated food frequency questionnaire. Evaluation of anthropometric profiles (body mass index, waist-hip ratio and percentage of body fat) was also evaluated. A questionnaire was applied to obtain information on the educational level and employment status of the patients. The CD4+ T-cell counts and viral loads of the same patients were determined using the flow cytometry and Polymerase Chain Reaction (PCR) method respectively. An association between educational level and dietary intake was significant (p < 0.05) for total dietary fibre, selenium and vitamin C. There was no significant (p > 0.05) association between the two socio-demographic variables (education and employment) and anthropometric profiles. The association between education, employment and CD4+ T-cell count was not significant (p > 0.05). The viral load showed a significant (p < 0.05) association with employment status but not correlated with education. The sample size or certain inherent biological and social factors probably affected the outcomes of the interplay between the two selected socio-demographic factors and the nutritional and immune status. It is suggested that the results of this study should be interpreted with caution. Further studies with larger sample sizes are recommended.

Changes in HIV prevalence and sexual behavior among men who have sex with men in a northern Chinese city: 2002-2006

OBJECTIVE

To examine HIV prevalence and sexual behavior changes among MSM in Harbin.

METHODS

Three community-based cross-sectional surveys among MSM were conducted based on the same protocol and methodology in 2002, 2004 and 2006 in Harbin, China. Men who were eligible were interviewed with a standard questionnaire. Urine samples were collected to screen their HIV status.

RESULTS

Among the MSM in Harbin, an increased trend was observed towards more self-identifying as homosexual (from 58% to 80%) and more living with a male partner (from 12% to 41%) over the study period. Although there was a trend towards a reduction in the rate of never using a condom and an increase in the rate of always using condoms during anal sex in the past six months, the prevalence of unprotected anal intercourse (UAI) was still at a high level (from 90% in 2002 to 72% in 2006). The HIV prevalence in 2006 (2.2%, 15/674) was higher than that in other study years, but no statistically significant change was detected.

CONCLUSIONS

Although an increase in condom use and a decline in drug use, STD infection and commercial sex have been monitored under current HIV prevention strategies, the MSM in Harbin is still highly vulnerable to HIV transmission given a high level of UAI and an increasing number of male sexual partners over the study period.

Assessing the feasibility of harm reduction services for MSM: the late night breakfast buffet study

BACKGROUND

Despite the leveling off in new HIV infections among men who have sex with men (MSM) in San Francisco, new evidence suggests that many recent HIV infections are linked with the use of Methamphetamine (MA). Among anonymous HIV testers in San Francisco, HIV incidence among MA users was 6.3% compared to 2.1% among non-MA users. Of particular concern for prevention programs are frequent users and HIV positive men who use MA. These MSM pose a particular challenge to HIV prevention efforts due to the need to reach them during very late night hours.

METHODS

The purpose of the Late Night Breakfast Buffet (LNBB) was to determine the feasibility and uptake of harm reduction services by a late night population of MSM. The "buffet" of services included: needle exchange, harm reduction information, oral HIV testing, and urine based sexually transmitted infection (STI) testing accompanied by counseling and consent procedures. The study had two components: harm reduction outreach and a behavioral survey. For 4 months during 2004, we provided van-based harm reduction services in three neighborhoods in San Francisco from 1-5 a.m. for anyone out late at night. We also administered a behavioral risk and service utilization survey among MSM.

RESULTS

We exchanged 2000 needles in 233 needle exchange visits, distributed 4500 condoms/lubricants and provided 21 HIV tests and 12 STI tests. Fifty-five MSM enrolled in the study component. The study population of MSM was characterized by low levels of income and education whose ages ranged from 18-55. Seventy-eight percent used MA in the last 3 months; almost 25% used MA every day in the same time frame. Of the 65% who ever injected, 97% injected MA and 13% injected it several times a day. MA and alcohol were strong influences in the majority of unprotected sexual encounters among both HIV negative and HIV positive MSM.

CONCLUSION

We reached a disenfranchised population of MA-using MSM who are at risk for acquiring or transmitting HIV infection through multiple high risk behaviors, and we established the feasibility and acceptability of late night harm reduction for MSM and MSM who inject drugs.

Population-level HIV declines and behavioral risk avoidance in Uganda

Uganda provides the clearest example that human immunodeficiency virus (HIV) is preventable if populations are mobilized to avoid risk. Despite limited resources, Uganda has shown a 70% decline in HIV prevalence since the early 1990s, linked to a 60% reduction in casual sex. The response in Uganda appears to be distinctively associated with communication about acquired immunodeficiency syndrome (AIDS) through social networks. Despite substantial condom use and promotion of biomedical approaches, other African countries have shown neither similar behavioral responses nor HIV prevalence declines of the same scale. The Ugandan success is equivalent to a vaccine of 80% effectiveness. Its replication will require changes in global HIV/AIDS intervention policies and their evaluation.

Viral load detectability profiles for HIV infection

The introduction of potent antiretroviral therapies for treatment of HIV infection typically results in a dramatic reduction in plasma HIV RNA concentration, often to levels undetectable by current measurement practices. However, although a high proportion of patients achieve 'undetectability', many then experience a return to a state of detectability at a later date. As evaluation of virologic response provides a useful measure of therapy efficacy, it is of interest to estimate the proportions of cases with undetectable viral load over time following commencement of treatment. These proportions depend on the rates of transition from detectability to undetectability and subsequent return to detectability, and may be related to covariates or risk factors, possibly differing in both transitions. We consider construction of detectability profiles as estimates of these proportions, based on parametric modelling of the component survival distributions. The method is applied to an examination of the effects of baseline CD4 T-cell lymphocyte counts on virologic response to therapy amongst patients of the Western Australian HIV Cohort Study.

HIV incidence in the United States, 1978-1999

CONTEXT

HIV incidence measurements, which reflect recent or current transmission, are valuable for monitoring the epidemic and evaluating prevention programs.

OBJECTIVES

To summarize HIV incidence patterns and trends in U.S. population groups.

DATA SOURCES

Publications in English from 1980 through mid-2000. STUDY SELECTION AND STATISTICAL METHODS: We searched the literature for reports of HIV incidence in the United States. Locally weighted scatterplot smoothing was used to generate smooth curves to estimate trends in incidence. Spearman rank correlation was used to estimate the correlation coefficient between prevalence and incidence.

DATA SYNTHESIS

In 74 eligible reports, HIV incidence varied widely (0.002-19.8 per 100 person-years [py]) depending on risk group. Among men who have sex with men (MSM), HIV incidence peaked in the early 1980s (5-20/100 py) and then declined but remained high during the 1990s (2-4/100 py). Among injection drug users (IDUs), incidence decreased since the mid-1980s but differed by geographic area; in the 1990s, incidence remained high in the East (1-3/100 py) but was lower in the West (<0.5/100 py). Throughout the late 1980s and 1990s, incidence was low and stable in broader populations (blood donors: <0.01/100 py; military personnel: 0.01-0.07/100 py). The correlation between HIV incidence and prevalence was strong in populations with a prevalence less than 1% (r = 0.94, p<.0001), moderate in populations with a prevalence from 1% to less than 10% (r = 0.57, p<.0001), and weak in populations with a prevalence at least 10% (r = 0.23, p=.09).

CONCLUSIONS

HIV prevention in the United States should continue to focus on MSM and IDUs. HIV incidence measurements should be considered for monitoring HIV transmission in MSM, IDUs, and other populations in which seroprevalence is high.

Incidence of human immunodeficiency virus among male-to-female transgendered persons in San Francisco

OBJECTIVE

To estimate HIV incidence among male-to-female transgendered persons (MtF transgendered persons) who repeatedly tested for HIV antibodies at public San Francisco counseling and testing sites between July 1997 and June 2000.

METHODS

HIV seroconversions were identified and person-time of observation were estimated using the date and result of the current test and the self-reported date and result of the previous test. Factors independently associated with HIV seroconversion were determined using multivariable proportional hazard analysis.

RESULTS

HIV incidence was 7.8 per 100 person-years (95% confidence intervals [CI], 4.6-12.3) based on 13 seroconversions among 155 repeat testers with 167.7 person-years of observation. African-American race/ethnicity (adjusted relative hazard ratio [HR], 5.0; 95% CI, 1.5-16.2) and unprotected receptive anal intercourse (HR, 3.9; 95% CI, 1.2-13.1) were independent predictors of HIV seroconversion.

CONCLUSIONS

HIV is currently spreading at an extremely high rate among MtF transgendered persons in San Francisco, especially those who are African Americans.

HIV-1 seroconversion in United States Army active duty personnel, 1985-1999

OBJECTIVE

To monitor HIV-1 infection trends among United States Army personnel, a predominantly young population group, tested between 1985 and 1999 for HIV-1 infection.

DESIGN

Demographic correlates of HIV-1 infection were assessed in the cohort via epidemiologic analysis.

METHODS

Annual seroconversion incidence rates were calculated per 1000 person-years (PY) of follow-up. Poisson regression was used to assess demographic correlates of HIV-1 seroconversion risk.

RESULTS

There were 1275 seroconverters among 2 004 903 active duty Army personnel accounting for 7 700 231 PY of follow-up. The HIV-1 incidence rate (IR) was 0.17/1000 PY [95% confidence interval (CI), 0.16-0.17]. The highest IR was observed in the first year of testing (IR, 0.43/1000 PY; 95% CI, 0.33-0.52). The IR for male and female soldiers was 0.18/1000 PY and 0.08/1000 PY, respectively. HIV-1 incidence declined with age. Significant risk of HIV-1 seroconversion was associated with age [> 30 years old relative risk (RR), 1.51], race (Black RR, 4.61; Hispanic RR, 2.76), gender (male RR, 3.12), marital status (unmarried RR, 2.01) and rank (enlisted RR, 2.50).

CONCLUSIONS

HIV-1 seroconversions in the US Army have been low and stable since the early 1990s. Continued HIV-1 incidence surveillance in the US Army provides information on the status of the epidemic in the Army, as well as important corroborative data on HIV-1 infections throughout the US.

Cofactors for HIV disease progression in a cohort of homosexual and bisexual men

To evaluate cofactors for progression of HIV infection, the authors identified 370 men with well-defined seroconversion dates and cofactor data among participants in the San Francisco City Clinic Cohort (SFCCC). Postseroconversion substance use, sexual behavior, and sexually transmitted diseases were assessed using multivariate proportional hazards models. Weekly use of hallucinogens strongly and independently predicted death (relative hazard [RH], 2.59; 95% confidence interval [CI], 1.56-4.28), as well as diagnosis of AIDS; weekly cocaine use also predicted mortality. Receptive anal intercourse with ejaculation was independently associated with mortality risk (RH, 1.45; 95% CI, 1.02-2.04) and AIDS. The associations of accelerated progression with weekly use of recreational drugs and unprotected receptive anal intercourse need to be confirmed in other prospective cohorts.

HIV seroincidence and risk factors among patients repeatedly tested for HIV attending sexually transmitted disease clinics in the United States, 1991 to 1996. STD Clinic HIV Seroincidence Study Group

To assess the incidence of HIV infection and risk factors associated with HIV seroconversion among patients attending clinics for sexually transmitted diseases (STD), medical record reviews were conducted in 12 clinics in 7 U.S. cities. The records of all patients who initially tested negative for HIV from 1991 through 1996 and who received at least one additional HIV test during the study period were reviewed. In each of 7 cities, 5 to 112 patients seroconverted. Of the 286 seroconverters identified in total, 53% (152 of 286) were heterosexual men and 28% (81 of 286) were women. HIV incidence rates among men who have sex with men (MSM) ranged by city from 0.81 to 7.0 new infections/100 person-years. Rates among heterosexual men and women ranged from 0.018 to 1.2 infections/100 person-years. Multivariate analyses showed that drug use was associated with HIV seroconversion only among heterosexuals. Most new HIV infections in these clinics are being transmitted heterosexually and are associated with drug use. Nevertheless, MSM, particularly young MSM, are at greatest risk for HIV in this population: 1 of 47 seroconvert/year. The effective use of targeted prevention efforts depends upon the continued ability to monitor the incidence of HIV infection.

Incidence of HIV and sexually transmitted diseases (STD) in a cohort of HIV-negative men who have sex with men (MSM)

OBJECTIVE

To determine the prevalence of sexually transmitted diseases (STD) and incidence of and risk factors for STD, including HIV-1, among a cohort of HIV-negative men who have sex with men (MSM).

SETTING

Seattle, Washington, United States.

PARTICIPANTS

Prospective cohort of 578 HIV-negative MSM in which risk factors for acquiring a STD over 12 months follow-up were evaluated using a cumulative incidence analysis.

MAIN OUTCOME MEASURES

Baseline tests obtained were: herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) Western blots, hepatitis B, and syphilis serologies; anorectal and pharyngeal Neisseria gonorrhoeae (GC) cultures; first-catch urine for leukocyte esterase (LE) and Chlamydia trachomatis (CT) ligase chain reaction (LCR). Men with a positive urine LE had urethral GC cultures obtained. The following outcomes were measured over 12 months follow-up: incident symptomatic bacterial STD (urethritis, proctitis, epididymitis), HSV-1 and HSV-2 seroconversion, and HIV-1 seroconversion. The 31 incident cases of STD (men with bacterial STD) were compared with those 489 men without symptomatic bacterial STD or seroconversion to HSV-1, HSV-2 or HIV-1 infection.

RESULTS

Bacterial STD were found in nine participants at enrollment; there were two cases of nonchlamydial urethritis, two cases of nonchlamydial epididymitis, and five cases of asymptomatic GC infection. At enrollment, HSV-2 antibodies were detected in 149 (26.0%) of 572 men and prior hepatitis B infection in 145 (34.8%) of 417 unvaccinated men. During the 1-year of follow-up, 31 men (5.7/100 person-years) had 34 episodes of a symptomatic bacterial STD syndrome (urethritis, epididymitis or proctitis). Urethritis was the most common STD syndrome, detected in 29 men, of whom 10 had GC and 19 had nongonococcal urethritis. In the 1-year of follow-up, five participants seroconverted to HIV-1 (1.3/100 person-years), four to HSV-2 (1.0/100 person-years), and seven to HSV-1 (4.3/100 person-years). Unprotected insertive anal sex [odds ratio (OR) 2.6; 95% confidence interval (CI) 1.2-5.6]; and nitrite inhalant ('poppers') use (OR, 2.3; 95% CI, 1.0-5.0) were independently associated with incident STD.

CONCLUSIONS

STD and HIV infection continue to be acquired even in a city with an overall low bacterial STD prevalence and among educated MSM receiving regular HIV screening and risk-reduction. Urethritis was the most common STD detected, and public health messages aimed at MSM need to emphasize safe insertive as well as receptive sexual practices.

Human immunodeficiency virus infection in pregnancy

The pace at which our knowledge and treatment of the human immunodeficiency virus (HIV) has advanced has been staggering. A disease that was unknown two decades ago, that was untreatable only a decade ago, and whose rate of mother-to-child transmission was immutable just 5 years ago, is now readily diagnosed, treated with increasing effectiveness, and blocked from transmission in the large majority of cases. None of these advances can be provided to patients unless their physicians actively screen patients and, for those identified as HIV infected, assure them of access to the latest therapies. This article is a primer for those obstetricians who would engage in such efforts. The data that form the basis of therapy are provided as well as clinical guidelines for the care of the pregnant woman infected with HIV.

Projected incidence of AIDS in San Francisco: the peak and decline of the epidemic

To predict the incidence of AIDS from 1978 through 1998 in San Francisco, we developed a model that combined annual HIV seroconversion rates for homosexual and bisexual men and for heterosexual injecting drug users with estimates of the incubation period distribution between HIV seroconversion and AIDS diagnosis and with estimates of the size of the at-risk populations. Our model assumed the availability of antiretroviral therapy at the efficacy level of zidovudine monotherapy. The annual number of new AIDS cases is estimated to have peaked at 3332 in 1992, and is projected to decline to 1196 annually by 1998. Although the projected number of cases decreased steadily during this period for homosexual and bisexual men, the projected number of cases for injection drug users, women, and persons with other risks increased between 1993 and 1998. The decline in the incidence of AIDS in San Francisco reflects the dramatic reductions in new HIV infections that occurred a decade previously and that were achieved as a result of significant changes in high-risk behaviors, primarily among homosexual and bisexual men. Changes in HIV seroincidence must be factored in before attributing the decrease in AIDS incidence to more effective combination antiretroviral treatment.

Incidence of HIV infection in a cohort of homosexually active men

The purpose of this study was to estimate the incidence of human immunodeficiency virus (HIV) in a cohort of homosexually active men in Sydney. In 1984-85 the Sydney AIDS Prospective Study enrolled homosexually active men, who were followed by six-monthly visits, although regular contact with most participants ceased in the early 1990s. In 1993-94 a major effort was made to establish the HIV status of all participants who had attended more than once. Of the 1075 men enrolled, 528 (49 per cent) were negative at enrollment and had at least one further documented HIV test. The annual incidence rate of HIV infection was highest in the early years of the study, 1984 (9.6 per cent) and 1986 (5.0 per cent), and remained low from 1987 (1.9 per cent) to 1994 (0.0 per cent). The incidence of HIV infection was higher among men aged under 34 years at enrollment and men who reported more than four sexual partners in the six months before enrollment, but these associations disappeared by 1987. The decrease in HIV incidence is consistent with findings from other cohorts followed for this length of time.

Markers, cofactors and staging systems in the study of HIV disease progression: a review

This paper is aimed at providing a comprehensive review of markers, cofactors and staging systems used for HIV disease, focusing on some aspects that nowadays could even be considered historical, and advancing in current issues such as the prognostic value of viral load measurements, viral genotypic and phenotypic characterization, and new HIV disease treatment protocols. CD4+ cell values, combined with the new viral markers mentioned are promising as a parsimonious predictor set for defining both severity and progression. An adequate predictor of patient resource use for planning purposes still needs to be defined.

Decreased incidence of sexually transmitted diseases among trucking company workers in Kenya: results of a behavioural risk-reduction programme

OBJECTIVE

To establish a cohort of high-risk individuals suitable for HIV-prevention trials, and to measure changes in sexual behaviour and sexually transmitted disease (STD) incidence after a behavioural intervention.

DESIGN

Prospective cohort study in trucking company depots in Mombasa, Kenya.

PARTICIPANTS

A total of 556 male HIV-seronegative employees of trucking companies.

INTERVENTIONS

HIV serological testing, individual counselling, condom promotion, STD diagnosis and management.

MAIN OUTCOME MEASURES

Sexual risk behaviour and symptomatic STD incidence.

RESULTS

Using time-trend modelling, significant declines in self-reported high-risk sexual behaviour were demonstrated during a 1-year follow-up. The percentage of men reporting any extramarital sex during the 3-month period prior to a follow-up visit decreased from 49% durig the first quarter of follow-up to 36% during the last quarter (P < 0.001). The decline in reported female sex worker contact was from 12% to 6% (P = 0.001). Approximately 30% of men reported consistent condom use during extramarital sex and this percentage remained unchanged during the study period. The incidence of STD declined from 34 per 100 person years (PY) during the first quarter to 10 per 100 PY during the last quarter (P = 0.001). Significant reductions in gonorrhoea (15 to five cases per 100 PY, P = 0.04), non-gonococcal urethritis (10 to two cases per 100 PY, P = 0.05), and genital ulcer disease (nine to two cases per 100 PY, P = 0.02) were observed.

CONCLUSIONS

Among truck company workers who participated in a cohort study in Mombasa, Kenya, there was a significant decrease in sex with high-risk partners, but no change in condom use. The change in heterosexual risk behaviour was accompanied by a significant decrease in incidence of gonorrhoea, non-gonococcal urethritis, and genital ulcer disease.

HIV-1 infection among female commercial sex workers in rural Thailand

OBJECTIVE

To reconstruct past HIV-1 incidence and identify risk factors for HIV-1 seroconversion among female commercial sex workers in a semi-rural setting in northern Thailand.

DESIGN

Retrospective cohort of sex workers attending a sexually transmitted disease (STD) clinic at Mae Chan District Hospital, Chiang Rai Province, Thailand.

METHODS

Information included demographic data, HIV-1 antibody testing and STD diagnosis was collected in 821 sex workers attending the STD clinic from 1989 through 1993. HIV-1 incidence among initially HIV-1-seronegative sex workers who underwent repeat HIV-1 antibody testing during follow-up was determined and possible predictive factors for seroconversion including diagnosis of other STD were examined.

RESULTS

HIV-1 seroprevalence among 556 sex workers who underwent antibody testing was 52%, rising from 29% at initial test in 1989 to 53-63% for 1990-1993. Among 96 initially HIV-1-negative sex workers who underwent repeat testing, 64 HIV-1 seroconversions occurred, giving an incidence rate of 12.6/100 person months (PM). Incidence increased from 12.0/100 PM for 1989 and 1990 to 17.0/100 PM for 1991, with a subsequent decline to 9.3/100 PM for 1992-1993. The cumulative risk of seroconversion 6 months following initial negative HIV-1 antibody test was 57%. There were higher rates among younger sex workers (14-19 years old) and those from Hilltribes, but only a diagnosis of chancroid was significantly associated with HIV-1 seroconversion (P = 0.014).

CONCLUSION

An explosive epidemic of HIV-1 occurred among sex workers in a semi-rural area of northern Thailand from 1989. These HIV-1 incidence estimates, which are among the highest rates of sexual transmission ever reported, highlight the extreme vulnerability of female sex workers to HIV infection, even in a non-urban setting.

Insurance type and satisfaction with medical care among HIV-infected men

Patient satisfaction is a valuable indicator of the quality of medical care. We assessed the impact of type of health insurance on satisfaction with seven aspects of medical care among 593 HIV-infected men without AIDS, drawn from three sites in San Francisco, California and Denver, Colorado. After adjustment for site of medical care, patient age, race, income, education, and CD4 lymphocyte count, there were few differences in satisfaction between men with fee-for-service and those with managed care insurance. Men with fee-for-service insurance were significantly more satisfied with their interpersonal relations with their clinicians (p = 0.01) but less satisfied with their finances (p = 0.0001) than persons with managed care. Uninsured men were significantly less satisfied with several aspects of care than insured persons. There were no significant differences in satisfaction between men with managed care and those with public insurance. HIV-infected persons who have a choice of insurance should carefully weigh their options, recognizing the implicit trade-offs between types of insurance. Those who choose fee-for-service insurance can expect to be more satisfied with interpersonal relations with their medical providers but less satisfied with financial aspects of their plans. Efforts to address the low satisfaction of uninsured persons are needed.

AIDS epidemic in San Francisco among men who report sex with men: successes and challenges of HIV prevention

San Francisco's gay male community has been hit harder by the HIV/AIDS epidemic than any other community in the world. By 1995, 20,530 of the estimated 58,000 gay men had been diagnosed with AIDS. However, the epidemic has also been more effectively contained within San Francisco than anywhere else, as evidenced by rapidly dropping AIDS incidence and mortality rates. This article reviews the epidemiology of HIV/AIDS among men who report sex with men (MSM) in San Francisco and the successful prevention efforts in this community. Also cited are areas in which the San Francisco prevention model has been less effective, in particular young MSM and gay men of color. San Francisco's experience yields many lessons about the successes and challenges of HIV prevention. Although community mobilization has been effective in reducing infection rates, innovative techniques to address the special needs of young MSM and to prevent the return to unsafe sex among all MSM are needed.

The UK register of HIV seroconverters: methods and analytical issues. UK register of HIV seroconverters (UKRHS) Steering Committee

A Register of HIV-infected persons who have had a negative antibody test within 3 years of their first antibody positive test (seroconverters) is being set up in the UK to monitor the distribution of times from HIV seroconversion to AIDS (the incubation period) and to death. It will also provide a national resource for use by those designing studies in this group of individuals. Clinicians caring for HIV-positive persons in Genito-Urinary Medicine, Infectious Disease and other departments throughout the UK were asked to participate by providing information on eligible subjects. Most laboratories undertaking HIV antibody testing were also contacted and asked to provide the name of the attending clinician for all seroconverters identified through the HIV laboratory reporting systems of the PHLS Communicable Disease Surveillance Centre (CDSC) and the Scottish Centre for Infection and Environmental Health (SCIEH) and for any other seroconverters known to them but not identified by CDSC or SCIEH. Data items sought for the Register include: sex, ethnic group, probable route of HIV transmission, annual CD4 counts, details of therapy and prophylaxis prescribed, AIDS-defining events and vital status. Follow up information is collected annually. Wherever possible, all seroconverters known to a clinic have been identified, whether currently alive or dead, either from clinic records or laboratory reporting or both. The objective is to establish and update a complete register of seroconverters on a long-term to basis to provide reliable estimates of the incubation period on which future projections of AIDS cases in the UK can be made.

Back-projection and sensitivity analysis of the HIV-AIDS epidemic in the Caribbean

In this study we estimated past human immunodeficiency virus (HIV) incidence in 19 nations in the primarily English-speaking Caribbean and projected the course of the epidemic to the year 1999. We compared the results obtained from several different models of HIV incidence and different assumed incubation distributions. Linear and nonlinear optimization methods were used to fit several models (power, logistic, spline, and step) to adult (age 15 years or older) AIDS incidence data derived from our existing surveillance system. All four models tested gave good fits to the data, with estimates of cumulative HIV incidence in 1993 ranging from 16,504 to 21,732. An increase in the assumed median of the AIDS incubation distribution by one year increased the estimates of current cumulative adult HIV incidence by approximately 12%; these estimates varied by as much as 6% between models. An adjustment of the data for possible reporting delay increased the estimates by approximately 7% and for underreporting by 25%. Despite their sensitivity to underlying assumptions, back-projection estimates provide useful insights into the patterns of HIV and AIDS incidence. The models indicate that HIV and AIDS incidences in the English-speaking Caribbean have been rising steadily, with adult HIV prevalence in the general population still less than 1%.

HIV-infected patients and dental care: nondisclosure of HIV status and rejection for treatment

OBJECTIVE

To investigate reports of nondisclosure of HIV-seropositivity to dentists by HIV-infected patients and their rejection for dental treatment.

STUDY DESIGN

An anonymous self-administered questionnaire was completed by 101 consecutive consenting HIV-infected patients.

RESULTS

Eighty percent of respondents (mean age, 36 years) had visited a dentist since their HIV diagnosis; 15% of these reported that they had been refused treatment because the dentist did not want to treat HIV-infected patients. Rejection was reported by 25% of respondents with heterosexual and 14% with homosexual risk factors, 11% of recipients of blood or blood products, and 8% with unknown or multiple risk factors. Refusal was not associated with economic factors. Nondisclosure of HIV-seropositivity to their current dentist was reported by 13% of respondents. No respondents attending hospitals or health units reported nondisclosure, compared with 18% of respondents attending private dental offices (p < 0.05).

CONCLUSION

More research is required with a larger sample to improve generalizability and to permit subgroup analysis.

A back-calculation method to estimate the age and period HIV infection intensity, considering the susceptible population

An extension of the back-calculation method to reconstruct the past history of HIV infections is presented. In this method the HIV infection intensity, as a function of age and calendar time, is assumed to belong to a family of parametric functions and is back-calculated from the observed AIDS incidence cases, knowledge of the incubation period and of the susceptible population, the final model being chosen as the one that gives the best fit. The model allows for the interaction between age and calendar time. The application to the main risk groups in Italy, male IVDUs and homosexuals, showed that age and the susceptible population were important in estimating the epidemic among IVDUs; interaction between age and calendar time was found to be significant, showing that among young IVDUs the risk of infection decreased faster than among older IVDUs. Sensitivity of the estimates to the assumption of population and choice of the infection function is investigated.

Does symptomatic primary HIV-1 infection accelerate progression to CDC stage IV disease, CD4 count below 200 x 10(6)/l, AIDS, and death from AIDS?

OBJECTIVE

To investigate the prognostic significance of symptomatic primary HIV-1 infection.

DESIGN

Prospective study of homosexual men seroconverting to HIV in 1985 and 1986. Patients were followed up at least three times yearly with clinical examinations and T cell subset determinations for an average of 7.2 years.

SETTING

Research project centred on attenders for treatment and screening for HIV at the Karolinska Institute, Stockholm.

SUBJECTS

19 patients presenting with a glandular-fever-like illness associated with seroconversion to HIV and 29 asymptomatic seroconverters.

MAIN OUTCOME MEASURES

Progression to Centers for Disease Control and Prevention stage IV disease, CD4 cell count below 200 x 10(6)/l, AIDS, and death from AIDS.

RESULTS

Symptomatic seroconverters were significantly more likely to develop Centers for Disease Control and Prevention stage IV disease (95% v 66%), CD4 cell counts below 200 x 10(6)/l (84% v 55%), and AIDS (58% v 28%) and die of AIDS (53% v 7%).

CONCLUSION

A glandular-fever-like illness associated with seroconversion to HIV-1 predicts accelerated progression to AIDS and other HIV related diseases.

A comparison of the progression rate to acquired immunodeficiency syndrome between intravenous drug users and homosexual men

In order to study differences in progression to Acquired Immunodeficiency Syndrome (AIDS) between risk groups, 205 homosexual men and 185 intravenous drug users (IVDUs) were followed from diagnosed seropositivity for Human Immunodeficiency Virus Type-1 (HIV) for a mean period of 46 months (range 1-88 months). Seven (4%) IVDUs and 55 homosexual men (27%) were diagnosed with AIDS during the follow-up period. The probability of being AIDS-free four years after diagnosed HIV positivity was 0.96 for IVDUs (SE 0.02) and 0.73 (SE 0.04) for homosexual men (p < 0.001, log rank test). When controlling for age and gender, the relative risk of AIDS progression for homosexual men was 9.1 (3.5-24.1, 95% confidence interval) as compared with IVDUs. Even when 24 months of follow-up time without progression were added for all homosexual men, assuming that the epidemic started two years earlier in this group, the relative risk of progression was 5.4 (2.1-14.4, 95% confidence interval) for homosexual men.

HIV infection in homosexual and bisexual men 18 to 29 years of age: the San Francisco Young Men's Health Study

OBJECTIVES

Recent studies suggest very high human immunodeficiency virus (HIV) infection rates in some populations of younger homosexual men, but these studies may represent only particularly high-risk populations. The current study obtained population-based data on the HIV epidemic in young homosexual/bisexual men.

METHODS

A household survey of unmarried men 18 through 29 years of age involved a multistage probability sample of addresses in San Francisco. A follow-up interview and HIV test for men who were HIV negative at baseline were completed; the median follow-up was 8.9 months.

RESULTS

Sixty-eight of 380 homosexual/bisexual men (17.9%) tested HIV seropositive. Sixty-three percent of men reported one or more receptive anal intercourse partners in the previous 12 months, and 41% of those men did not use condoms consistently. The HIV seroincidence rate among those seronegative at first study was 2.6% per year.

CONCLUSIONS

HIV infection rates in young homosexual men in San Francisco are lower than those in the early 1980s; however, the rate of infection in these men, most of whom became sexually active after awareness of AIDS had become widespread, threatens to continue the epidemic in the younger generation at a level not far below that of a decade ago.

The effectiveness of interventions on incubation of AIDS as measured by secular increases within a population

Methods are developed to estimate and test for the impact of intervention use on a population's survival function (time to AIDS). Each participant's history is divided into J + 1 components: omega 0 occurring before the intervention is available and omega 1 to omega J occurring later, as the intervention becomes successively more available. Distribution free truncated Kaplan-Meier models based on time since exposure fit separately to the risk sets/outcomes in omega 0 to omega J directly show the changing patterns of survival. Multivariate proportional hazards models can be used to adjust for covariates. Application of these methods indicates that availability of proven anti-AIDS interventions may have delayed time to AIDS by 8 months in an educated HIV-1 infected homosexual cohort with good access to medical care.

Epidemiologic background and long-term course of disease in human immunodeficiency virus type 1-infected blood donors identified before routine laboratory screening. Transfusion Safety Study Group

BACKGROUND

The long-term course of human immunodeficiency virus type 1 (HIV-1)-related disease among seropositive blood donors has not been described. The enrollment and epidemiologic background of HIV-1-infected donors in the Transfusion Safety Study and their immunologic and clinical progression are described.

STUDY DESIGN AND METHODS

Through the testing of approximately 200,000 sera from donations made in late 1984 and early 1985, 146 anti-HIV-1-positive donors and 151 uninfected matched donors were enrolled. These two cohorts were followed with 6-month interval histories and laboratory testing.

RESULTS

Seropositive donors detected before the institution of routine anti-HIV-1 screening disproportionately were first-time donors and men with exclusively male sexual contacts. The actuarial probability of a person's developing AIDS within 7 years after donation was 40 percent; the probability of a person's dying of AIDS was 28 percent. AIDS developed more often when the donor was p24 antigen-positive at donation. Over a 3-year period, significant decreases occurred in CD4+, CD2+CD26+, CD4+CD29+, and CD20+CD21+ counts, but not in CD8+ subsets, CD20+, or CD14+.

CONCLUSION

The high proportions of first-time donations and exclusively homosexual men among seropositive donors suggest that test-seeking may have contributed to the high HIV-1 prevalence in the repository. Implementation of alternative test sites when routine donor screening began in 1985 may have averted many high-risk donations. The disease course in HIV-1-infected donors had the same wide spectrum of immunologic and clinical manifestations as were reported for other cohorts.

The prevalence of informal caregiving to persons with AIDS in the United States: caregiver characteristics and their implications

Based on U.S. national (N = 2673) and central cities (N = 8263) probability samples, this paper: (1) presents estimates of the proportion of the United States population that has provided informal care to persons with AIDS; (2) identifies socio-demographic characteristics of 'typical' AIDS caregivers in the U.S.; and (3) discusses social, economic and health-related implications of informal caregiving to persons with AIDS. Results indicate that 5.0% of all adults age 18-75 living within central cities and 3.2% of the entire adult U.S. population have provided care to a friend, relative or lover with AIDS. Although caregivers are distributed throughout different age and ethnic groups, the majority of caregivers are younger (< 40 years) and white. Males, gay and bisexual men in particular are over-represented among central cities caregivers. Data on the types of caregiving tasks performed show that 64.4% of all caregivers within central cities perform domestic types of caregiving tasks, while 27.7% are involved in personal care of AIDS patients. Caregivers are more likely than non-caregivers to have been tested for HIV, and among the tested, caregivers are more likely to have tested positive. While informal caregiving reduces costs to the formal medical sector, costs to the caregivers themselves should be considered. Physical and emotional stress, as well as reduced opportunity for social and economic development, represent potential outcomes of caregiving. Socio-demographic characteristics of AIDS caregivers, such as their typically young age, suggest that these caregivers may be at particular risk for detrimental consequences.

Estimation of time since infection using longitudinal disease-marker data

We propose a method to estimate the usually unknown time since infection for individuals infected with human immunodeficiency virus type 1 (HIV-1). If we assume the time since infection has an exponential prior distribution, then under the model the conditional distribution of time since infection, given the CD4 level at the time of the first positive HIV-1 antibody test, is a truncated normal density. We applied the method to prevalent cohort data both from intravenous drug users and from homosexual/bisexual men. For the intravenous drug users the estimated mean time since infection was 15.0 months from infection at a presumed mean CD4 level of 1060 cells/ml to first positive antibody test at a CD4 level of 597 cells/ml, which was the average CD4 at enrollment for infected subjects. For the homosexual/bisexual men the estimated mean time since infection was 16.7 months from infection at a presumed mean CD4 level of 699 cells/ml to first positive antibody test at an average CD4 level of 577 cells/ml. We performed a validation study using initially seronegative subjects in these cohorts who seroconverted to HIV-1-positive antibody status during the follow-up period. For the intravenous drug users, data were too few to provide definitive verification of the method. In the cohort of homosexual/bisexual men, however, there was a total of 70 seroconverters with relevant data. Among them, the median absolute difference between the midpoint of the known seroconversion interval and the estimated mean infection date was 4.6 months, conditional on CD4-lymphocyte measurements taken approximately 18 months subsequent to infection. Conditional on CD4 approximately 30 months after infection, this median difference increased modestly to 8.2 months. Our analysis suggested that the underlying mathematical model tends to overestimate short times since infection and underestimate long times since infection. We consider potential corrective modifications to the model.

Maturity of human immunodeficiency virus infection and incubation period of acquired immunodeficiency syndrome in injecting drug users

This study was aimed at estimating the maturity of the human immunodeficiency virus (HIV) epidemic in cohorts of injecting drug users with existing HIV infection at the time of first observation, and using this information to estimate the incubation period of acquired immunodeficiency syndrome (AIDS) in this population group. The method imputed the "missing" time from seroconversion to first observation for seroprevalent subjects in a combined cohort including injecting drug users from New York (n = 246) and Baltimore (n = 621). Imputation relied on a probability model predicting time since seroconversion on the basis of two markers of maturity of HIV infection: percent of CD4+ lymphocytes and platelet count. The model was developed from data observed in a combined cohort of subjects from New York (n = 24) and Baltimore (n = 112) who had incident HIV infections. The estimates of median time since seroconversion for the Baltimore and Bronx seroprevalent subcohorts were 28 and 39 months, respectively. The total time from seroconversion to AIDS was then estimated for the incident plus completed-prevalent cohorts using a modified version of the nonparametric product-limit method. The results showed that approximately 95% (95% confidence interval: 90 to 98%) of drug users remained AIDS-free 2 years after seroconversion; 83% (74-91%), 4 years after seroconversion; and 72% (61-82%), 6 years after seroconversion. Median time to AIDS was 10.2 years, with an estimated 95% confidence interval of 7.9 to 12.3 years. Consistency of these results with those derived from large cohorts of homosexual men indicate that the HIV incubation distributions for drug users and homosexual men are similar.

Falling incidence of HIV infection in a cohort of clinic attenders

It is widely accepted that changes in sexual behaviour in the mid-1980s drastically reduced the spread of human immunodeficiency virus (HIV) through male homosexual contact in Western countries, but documentation of changes in infection rates has been based on observation of subjects enrolled in cohort studies, who may be highly selected and motivated. In this study, the incidence of HIV seroconversion was investigated among people attending a major site of HIV testing, counselling and patient care in Sydney. Over the period March 1985 to June 1990, 2,301 people were tested for HIV antibody on more than one occasion, following a negative result at the first test. On the basis of subsequent tests, 107 were found to have seroconverted during the study period, including 91 men who reported homosexual or bisexual contact as their only exposure to HIV. Overall, the incidence rate of HIV infection among men reporting homosexual or bisexual contact was 404 per 100 person-years of follow-up. Under various methods of calculation, the incidence was estimated to have declined between 1985 and 1989-1990. However, there was continuing HIV seroconversion in 1989-1990 and no indication of declining incidence in younger men. The fall in HIV incidence documented in this study supports the role of HIV prevention programs aimed at homosexual and bisexual men.

Smoothed nonparametric back-projection of AIDS incidence data with adjustment for therapy

Back-projection is a major tool for assessing the extent of the HIV epidemic. Its application relies on a model for the incubation period of AIDS into which the administration and effect of therapy has been incorporated. We propose a compartmental model with proportional transition rates to describe variation and changes in the duration of the incubation period. The model is easily related to available data and offers fast computation. Its detailed and direct reflection of the administration and effect of therapy makes it relatively easy to ensure that therapy has been accommodated to an appropriate extent. The effect of therapy on back-projection estimates of the HIV epidemic curve is demonstrated with an application to Australian AIDS incidence data.

Use of backcalculation for estimation of the probability of progression from HIV infection to AIDS

Backcalculation has been used to estimate the rate of past HIV infection and to predict future AIDS incidence. In this study we examine another use: estimating the probability of progression from HIV infection to AIDS as a function of time from infection. Given observed AIDS incidence data, the technique of backcalculation estimates the most likely number of persons infected with HIV in the past. Assumptions about probability of progression from HIV infection to AIDS are necessary. By varying these assumptions and examining the resulting goodness of fit to the AIDS incidence data, we can theoretically estimate parameters of progression. We report on implementation of this method and examine its practical utility in deciding among four competing progression models specified on a priori grounds. The four specific models comprise three Weibull distributions with medians of 8, 10, and 12 years, respectively, and one model that begins as a Weibull with 8 year median but where the hazard is level after 3.5 years. To employ asymptotic maximum likelihood methods, we define a two parameter family of progression models that includes all four a priori models. One parameter sets the scale for an initial Weibull progression (the shape parameter being fixed for all models), and the other specifies a levelling point after which the hazard remains constant. AIDS incidence data from Canada's national surveillance system provided the empiric data for this evaluation. First we corrected these data for reporting delay by Poisson modelling of the delay distribution. We used three parametric families of infection curves: step-function, log-logistic, and logistic. The results support the hypothesis of an early levelling of the hazard function. When we fixed the scale parameter to that of the Weibull curve with 8 year median, the maximum likelihood estimate of the levelling point was 2.7 years, and a clearly superior fit was produced compared to a pure Weibull progression with the same scale parameter (likelihood ratio chi-square of 10.6 on 1 degree of freedom, p = 0.001). The maximum was indistinguishable in fit from the levelling point of 3.5 years hypothesized in advance (chi-square = 0.30, d.f. = 1, p = 0.58). Backcalculation, however, could not determine the Weibull scale parameter itself because the likelihood was quite flat as a function of this parameter. We conclude that one must determine the parameters governing the initial shape of the hazard function from other kinds of data.(ABSTRACT TRUNCATED AT 400 WORDS)

Different AIDS incubation periods and their impacts on reconstructing human immunodeficiency virus epidemics and projecting AIDS incidence

The objective of this study was to investigate heterogeneity in incubation distributions in different cohorts and to assess the sensitivity of back-calculated infection rates to different assumptions about incubation times from human immunodeficiency virus (HIV) infection to AIDS diagnosis. Incubation distributions were estimated by using data from three different cohort studies. These and one other published incubation model were used as inputs for a back-calculation procedure that reconstructed smooth HIV-infection rates from AIDS incidence among adults in the United States, allowing for changes over time in incubation. Incubation estimates from the different cohorts differed substantially. The cumulative HIV incidence estimates that result from using the different incubations are very different, but the back-calculated models all produce good fits to the observed diagnosis counts. We conclude that systematic differences in incubation times of different groups add substantially to the uncertainty inherent in using the back-calculation method to reconstruct HIV epidemics and project future numbers of AIDS cases.