HIV among People Who Inject Drugs in the Middle East and North Africa: Systematic Review and Data Synthesis

Background

It is perceived that little is known about the epidemiology of HIV infection among people who inject drugs (PWID) in the Middle East and North Africa (MENA). The primary objective of this study was to assess the status of the HIV epidemic among PWID in MENA by describing HIV prevalence and incidence. Secondary objectives were to describe the risk behavior environment and the HIV epidemic potential among PWID, and to estimate the prevalence of injecting drug use in MENA.

Methods and Findings

This was a systematic review following the PRISMA guidelines and covering 23 MENA countries. PubMed, Embase, regional and international databases, as well as country-level reports were searched up to December 16, 2013. Primary studies reporting (1) the prevalence/incidence of HIV, other sexually transmitted infections, or hepatitis C virus (HCV) among PWIDs; or (2) the prevalence of injecting or sexual risk behaviors, or HIV knowledge among PWID; or (3) the number/proportion of PWID in MENA countries, were eligible for inclusion. The quality, quantity, and geographic coverage of the data were assessed at country level. Risk of bias in predefined quality domains was described to assess the quality of available HIV prevalence measures. After multiple level screening, 192 eligible reports were included in the review. There were 197 HIV prevalence measures on a total of 58,241 PWID extracted from reports, and an additional 226 HIV prevalence measures extracted from the databases.We estimated that there are 626,000 PWID in MENA (range: 335,000–1,635,000, prevalence of 0.24 per 100 adults). We found evidence of HIV epidemics among PWID in at least one-third of MENA countries, most of which are emerging concentrated epidemics and with HIV prevalence overall in the range of 10%–15%. Some of the epidemics have however already reached considerable levels including some of the highest HIV prevalence among PWID globally (87.1% in Tripoli, Libya). The relatively high prevalence of sharing needles/syringes (18%–28% in the last injection), the low levels of condom use (20%–54% ever condom use), the high levels of having sex with sex workers and of men having sex with men (15%–30% and 2%–10% in the last year, respectively), and of selling sex (5%–29% in the last year), indicate a high injecting and sexual risk environment. The prevalence of HCV (31%–64%) and of sexually transmitted infections suggest high levels of risk behavior indicative of the potential for more and larger HIV epidemics.

Conclusions

Our study identified a large volume of HIV-related biological and behavioral data among PWID in the MENA region. The coverage and quality of the data varied between countries. There is robust evidence for HIV epidemics among PWID in multiple countries, most of which have emerged within the last decade and continue to grow. The lack of sufficient evidence in some MENA countries does not preclude the possibility of hidden epidemics among PWID in these settings. With the HIV epidemic among PWID in overall a relatively early phase, there is a window of opportunity for prevention that should not be missed through the provision of comprehensive programs, including scale-up of harm reduction services and expansion of surveillance systems. Please see later in the article for the Editors'' Summary     

Comparison of female to male and male to female transmission of HIV in 563 stable couples. European Study Group on Heterosexual Transmission of HIV.

OBJECTIVE--To identify risk factors for heterosexual transmission of HIV and to compare the efficiency of male to female and female to male transmission. DESIGN--Cohort study of heterosexual couples. Regular partners of HIV infected subjects were tested and both members of the couples interviewed every six months. HIV prevalence in partners was analysed according to the characteristics of the couples. SETTING--Nine European countries. SUBJECTS--563 couples comprising 156 female index patients with their 159 male partners and 400 male index patients with their 404 female partners. Partners reporting risk factors other than sexual contacts with the index patient were excluded. MAIN OUTCOME MEASURES--HIV infection in partners and high risk sexual behaviour. RESULTS--Overall, 19 (12%) male partners and 82 (20%) female partners were infected with HIV, suggesting that male to female transmission is 1.9 (95% confidence interval 1.1 to 3.3) times more effective than female to male transmission. An advanced stage of HIV infection in the index patient (odds ratio 17.6; 4.9 to 62.7) and sexual contacts during menses (3.4; 1.0 to 11.1) increased the risk of female to male transmission and stage of infection (2.7; 1.5 to 4.9), anal sex (5.1; 2.9 to 8.9), and age of the female partner (3.9; 1.2 to 13.0 for age > 45 years) increased the risk of male to female transmission. None of the 24 partners who had used condoms systematically since the first sexual contact was infected. CONCLUSIONS--Several factors which potentiate the risk of transmission through unprotected vaginal intercourse have been identified. Knowledge of these factors could be helpful for counselling patients infected with HIV and their sexual partners.     

Are HIV Epidemics among Men Who Have Sex with Men Emerging in the Middle East and North Africa?: A Systematic Review and Data Synthesis

Background

Men who have sex with men (MSM) bear a disproportionately higher burden of HIV infection than the general population. MSM in the Middle East and North Africa (MENA) are a largely hidden population because of a prevailing stigma towards this type of sexual behavior, thereby limiting the ability to assess infection transmission patterns among them. It is widely perceived that data are virtually nonexistent on MSM and HIV in this region. The objective of this review was to delineate, for the first time, the evidence on the epidemiology of HIV among MSM in MENA.

Methods and Findings

This was a systematic review of all biological, behavioral, and other related data on HIV and MSM in MENA. Sources of data included PubMed (Medline), international organizations'' reports and databases, country-level reports and databases including governmental and nongovernmental organization publications, and various other institutional documents. This review showed that onsiderable data are available on MSM and HIV in MENA. While HIV prevalence continues at low levels among different MSM groups, HIV epidemics appear to be emerging in at least few countries, with a prevalence reaching up to 28% among certain MSM groups. By 2008, the contribution of MSM transmission to the total HIV notified cases increased and exceeded 25% in several countries. The high levels of risk behavior (4–14 partners on average in the last six months among different MSM populations) and of biomarkers of risks (such as herpes simplex virus type 2 at 3%–54%), the overall low rate of consistent condom use (generally below 25%), the relative frequency of male sex work (20%–76%), and the substantial overlap with heterosexual risk behavior and injecting drug use suggest potential for further spread.

Conclusions

This systematic review and data synthesis indicate that HIV epidemics appear to be emerging among MSM in at least a few MENA countries and could already be in a concentrated state among several MSM groups. There is an urgent need to expand HIV surveillance and access to HIV testing, prevention, and treatment services in a rapidly narrowing window of opportunity to prevent the worst of HIV transmission among MSM in the Middle East and North Africa. Please see later in the article for the Editors'' Summary     

Host-pathogen interactions, insect outbreaks, and natural selection for disease resistance

The theory of insect population dynamics has shown that heterogeneity in natural-enemy attack rates is strongly stabilizing. We tested the usefulness of this theory for outbreaking insects, many of which are attacked by infectious pathogens. We measured heterogeneity among gypsy moth larvae in their risk of infection with a nucleopolyhedrovirus, which is effectively heterogeneity in the pathogen's attack rate. Our data show that heterogeneity in infection risk in this insect is so high that it leads to a stable equilibrium in the models, which is inconsistent with the outbreaks seen in North American gypsy moth populations. Our data further suggest that infection risk declines after epidemics, in turn suggesting that the model assumption of constant infection risk is incorrect. We therefore constructed an alternative model in which natural selection drives fluctuations in infection risk, leading to reductions after epidemics because of selection for resistance and increases after epidemics because of a cost of resistance. This model shows cycles even for high heterogeneity, and experiments confirm that infection risk is indeed heritable. The model is very general, and so we argue that natural selection for disease resistance may play a role in many insect outbreaks.     

Factors Associated with Change in Sexual Transmission Risk Behavior over 3 Years among HIV-Infected Patients in Tanzania

Background

The reduction of HIV transmission risk behaviors among those infected with HIV remains a major global health priority. Psychosocial characteristics have proven to be important correlates of sexual transmission risk behaviors in high-income countries, but little attention has focused on the influence of psychosocial and psychological factors on sexual transmission risk behaviors in African cohorts.

Methodology and Principal Findings

The CHAT Study enrolled a representative sample of 499 HIV-infected patients in established HIV care and 267 newly diagnosed HIV-infected individuals from the Kilimanjaro Region of Tanzania. Participants completed in-person interviews every 6 months for 3 years. Using logistic random effects models to account for repeated observations, we assessed sociodemographic, physical health, and psychosocial predictors of self-reported unprotected sexual intercourse. Among established patients, the proportion reporting any recent unprotected sex was stable, ranging between 6–13% over 3 years. Among newly diagnosed patients, the proportion reporting any unprotected sex dropped from 43% at baseline to 11–21% at 6–36 months. In multivariable models, higher odds of reported unprotected sex was associated with female gender, younger age, being married, better physical health, and greater post-traumatic stress symptoms. In addition, within-individual changes in post-traumatic stress over time coincided with increases in unprotected sex.

Conclusions and Significance

Changes in post-traumatic stress symptomatology were associated with changes in sexual transmission risk behaviors in this sample of HIV-infected adults in Tanzania, suggesting the importance of investing in appropriate mental health screening and intervention services for HIV-infected patients, both to improve mental health and to support secondary prevention efforts.     

The epidemiology of HIV and AIDS in the world

The worldwide epidemic of HIV continues to expand in many regions of the world, particularly in southern Africa, South and Southeast Asia, East Asia and Eastern Europe and Central Asia. Estimates are that at the end of 2005 there were 38.6 million persons living with HIV infection and that 4.1 million new infections and 2.8 million deaths from HIV occurred during the year. Regionally different patterns predominate from generalized heterosexual epidemics in sub-Saharan Africa and parts of the Caribbean to mixes of epidemics in which transmission among injection drug users, their sexual partners, commercial sex workers and their partners intersect. Multilateral and bilateral antiretroviral access campaigns, such as the World Health Organization's 3 x 5 initiative, have resulted in broader access to live-saving therapy for infected persons in low- and middle-income countries, but several million infected people who are clinically eligible for antiretroviral therapy remain untreated. The public health challenge worldwide is to keep the uninfected and to treat and care for those who have already been infected.     

The HIV-poverty thesis re-examined: poverty, wealth or inequality as a social determinant of HIV infection in sub-Saharan Africa?

Although health is generally believed to improve with higher wealth, research on HIV in sub-Saharan Africa has shown otherwise. Whereas researchers and advocates have frequently advanced poverty as a social determinant that can help to explain sub-Saharan Africa's disproportionate burden of HIV infection, recent evidence from population surveys suggests that HIV infection is higher among wealthier individuals. Furthermore, wealthier countries in Africa have experienced the fastest growing epidemics. Some researchers have theorized that inequality in wealth may be more important than absolute wealth in explaining why some countries have higher rates of infection and rapidly increasing epidemics. Studies taking a longitudinal approach have further suggested a dynamic process whereby wealth initially increases risk for HIV acquisition and later becomes protective. Prior studies, conducted exclusively at either the individual or the country level, have neither attempted to disentangle the effects of absolute and relative wealth on HIV infection nor to look simultaneously at different levels of analysis within countries at different stages in their epidemics. The current study used micro-, meso- and macro-level data from Demographic and Health Surveys (DHS) across 170 regions within sixteen countries in sub-Saharan Africa to test the hypothesis that socioeconomic inequality, adjusted for absolute wealth, is associated with greater risk of HIV infection. These analyses reveal that inequality trumps wealth: living in a region with greater inequality in wealth was significantly associated with increased individual risk of HIV infection, net of absolute wealth. The findings also reveal a paradox that supports a dynamic interpretation of epidemic trends: in wealthier regions/countries, individuals with less wealth were more likely to be infected with HIV, whereas in poorer regions/countries, individuals with more wealth were more likely to be infected with HIV. These findings add additional nuance to existing literature on the relationship between HIV and socioeconomic status.     

Transitions from injection-drug-use-concentrated to self-sustaining heterosexual HIV epidemics: patterns in the international data

Background

Injecting drug use continues to be a primary driver of HIV epidemics in many parts of the world. Many people who inject drugs (PWID) are sexually active, so it is possible that high-seroprevalence HIV epidemics among PWID may initiate self-sustaining heterosexual transmission epidemics.

Methods

Fourteen countries that had experienced high seroprevalence (<20%) HIV epidemics among PWID and had reliable data for injection drug use (IDU) and heterosexual cases of HIV or AIDS were identified. Graphs of newly reported HIV or AIDS cases among PWID and heterosexuals were constructed to identify temporal relationships between the two types of epidemics. The year in which newly reported cases among heterosexuals surpassed newly reported cases among PWID, aspects of the epidemic curves, and epidemic case histories were analyzed to assess whether it was “plausible” or “highly unlikely” that the HIV epidemic among PWID might have initiated the heterosexual epidemic in each country.

Results

Transitions have occurred in 11 of the 14 countries. Two types of temporal relationships between IDU and heterosexual HIV epidemics were identified, rapid high incidence transitions vs. delayed, low incidence transitions. In six countries it appears “plausible” that the IDU epidemic initiated a heterosexual epidemic, and in five countries it appears “highly unlikely” that the IDU epidemic initiated a heterosexual epidemic. A rapid decline in incidence among PWID after the peak year of new cases and national income were the best predictors of the “highly unlikely” initiation of a heterosexual epidemic.

Discussion

Transitions from IDU concentrated epidemics to heterosexual epidemics are common in countries with high seroprevalence among PWID though there are distinct types of transitions. Interventions to immediately reduce HIV incidence among PWID may reduce the likelihood that an IDU epidemic may initiate a heterosexual epidemic.     

The 2001-03 Famine and the Dynamics of HIV in Malawi: A Natural Experiment

Background

Food security has deteriorated for many people in developing regions facing high and volatile food prices. Without effective and equitable responses, the situation is likely to worsen due to diminishing access to land and water, competition from non-food uses of agricultural products, and the effects of climate change and variability. Understanding how this will affect the burden and distribution of major diseases such as HIV is critical. This study makes use of the near-experimental conditions created by the Malawi famine to shed new light on this issue.

Methods

Multilevel, random intercept models were used to relate the change in HIV prevalence at antenatal surveillance sites over the course of the famine to the proportion of rural households requiring food aid in the surrounding district at the famine’s peak. Similar models were used to relate this indicator of rural hunger to changes in the composition of the antenatal population. The extent and direction of migration were estimated from a household survey conducted 1–2 years after the famine.

Findings

At rural sites, the change in HIV prevalence was positively and non-linearly related to the extent of rural hunger (P = 0.016), consistent with contemporary accounts of increased transactional sex and with hunger compromising immune function. At non-rural sites, prevalence declined as rural hunger increased (P = 0.006), concentrated in women who self-identified as farmers (P = 0.010). This finding is consistent with contemporary accounts of migration in search of food and work from villages where HIV risk was lower to towns and cities where it was higher. Corroborating this interpretation, the proportion of farmers in the antenatal population was found to rise at non-rural sites as rural hunger increased in the surrounding district (P = 0.015) whereas the proportion fell with increasing rural hunger at rural sites (P<0.001). The models suggest migrants were predominantly farming women under 25 years (P = 0.010). The household survey confirmed that there was a surge of rural-to-urban migration during the famine, particularly by women under 25 years. Migration to less affected rural areas also increased.

Conclusion

The Malawi famine appears to have had a substantial effect on HIV’s dynamics and demography. Poverty and inequality, commonly considered structural determinants of HIV epidemics, can change rapidly, apparently transmitting their effects with little lag. Epidemic patterns risk being misread if such social and economic change is ignored. Many studies examining HIV prevalence declines have implicated sexual behaviour change but do not appear to have adequately considered the contribution of rural-urban migration. The evidence from Malawi, which links actions that undermined people’s food security to changes in the prevalence and distribution of HIV infections, suggests new opportunities for prevention.     

Assessing the Potential Impact of Hormonal-Based Contraceptives on HIV Transmission Dynamics Among Heterosexuals

HIV susceptibility linked to hormonal contraception (HC) has been studied before, but with mixed results. Reports from some of the recent findings have prompted the World Health Organisation to encourage women who use HC to concurrently use condoms in order to prevent HIV infection in the light of possible increased HIV risk of infection associated with hormone-based contraceptives. A two-sex HIV model classifying women into three risk groups consisting of individuals who use condoms, natural methods, and hormone-based contraceptives is formulated and analysed to assess the possible effects of various birth control strategies on the transmission dynamics of the disease. Our model results showed that women who use HC could be key drivers of the epidemic and that their increased infectivity may be critical in driving the epidemic. Women who use hormone-based contraceptives potentially act as a core group from which men get infected and in turn transmit the disease to other population groups. We fitted the model to HIV prevalence data for Zimbabwe reported by UNAIDS and Zimbabwe Ministry of Health and Child Care and used the model fit to project HIV prevalence. Predictions using HIV data for Zimbabwe suggest that a hypothesised increase in susceptibility and infectivity of two-, three-, and fourfold would result in a 25, 50, and 100% increase in baseline HIV prevalence projection, respectively, thus suggesting possible increased disease burden even in countries reporting plausible HIV prevalence declines. Although a possible causal relationship between HIV susceptibility and HC use remains subject of continuing scientific probe, its inclusion as part of birth control strategy has been shown in this study, to possibly increase HIV transmission. If proven, HC use may potentially explain the inordinate spread of HIV within the sub-Saharan Africa region and therefore compel for urgent assessment with a view to reorienting birth control methods in use in settings with generalised epidemics.     

Are You HIV Invincible? A Probabilistic Study of Discordant Couples in the Context of HIV Transmission

A number of factors have been identified that are related to sexual and injecting HIV transmission. We developed a probabilistic mathematical model to put these factors together and interpret risks in the context of individual behavior among injecting drug-using (IDU) couples in St. Petersburg, Russia. Some HIV-discordant couples have unprotected sex and sometimes inject drugs together but stay discordant for a long time, while some individuals acquire HIV on the first encounter. We considered existing estimates of HIV transmission risks through injecting and sexual contacts to develop a predictive survival model for an individual who is exposed to HIV through intimate relationships. We computed simulated survival curves for a number of behavioral scenarios and discussed sources of simulated uncertainty. We then applied the model to a longitudinal study of HIV-discordant couples and validated the model’s forecast. Although individual prediction of seroconversion time appeared impossible, the ability to rank behavioral patterns in terms of HIV risk and to estimate the probability of survival HIV-free will be important to educators and counselors.     

Modeling the joint epidemics of TB and HIV in a South African township

We present a simple mathematical model with six compartments for the interaction between HIV and TB epidemics. Using data from a township near Cape Town, South Africa, where the prevalence of HIV is above 20% and where the TB notification rate is close to 2,000 per 100,000 per year, we estimate some of the model parameters and study how various control measures might change the course of these epidemics. Condom promotion, increased TB detection and TB preventive therapy have a clear positive effect. The impact of antiretroviral therapy on the incidence of HIV is unclear and depends on the extent to which it reduces sexual transmission. However, our analysis suggests that it will greatly reduce the TB notification rate.     

Predicting the impact of a nonsterilizing vaccine against human immunodeficiency virus

Studies of human immunodeficiency virus (HIV) vaccines in animal models suggest that it is difficult to induce complete protection from infection (sterilizing immunity) but that it is possible to reduce the viral load and to slow or prevent disease progression following infection. We have developed an age-structured epidemiological model of the effects of a disease-modifying HIV vaccine that incorporates the intrahost dynamics of infection, a transmission rate and host mortality that depend on the viral load, the possible evolution and transmission of vaccine escape mutant viruses, a finite duration of vaccine protection, and possible changes in sexual behavior. Using this model, we investigated the long-term outcome of a disease-modifying vaccine and utilized uncertainty analysis to quantify the effects of our lack of precise knowledge of various parameters. Our results suggest that the extent of viral load reduction in vaccinated infected individuals (compared to unvaccinated individuals) is the key predictor of vaccine efficacy. Reductions in viral load of about 1 log(10) copies ml(-1) would be sufficient to significantly reduce HIV-associated mortality in the first 20 years after the introduction of vaccination. Changes in sexual risk behavior also had a strong impact on the epidemic outcome. The impact of vaccination is dependent on the population in which it is used, with disease-modifying vaccines predicted to have the most impact in areas of low prevalence and rapid epidemic growth. Surprisingly, the extent to which vaccination alters disease progression, the rate of generation of escape mutants, and the transmission of escape mutants are predicted to have only a weak impact on the epidemic outcome over the first 25 years after the introduction of a vaccine.     

Genital herpes has played a more important role than any other sexually transmitted infection in driving HIV prevalence in Africa

Background

Extensive evidence from observational studies suggests a role for genital herpes in the HIV epidemic. A number of herpes vaccines are under development and several trials of the efficacy of HSV-2 treatment with acyclovir in reducing HIV acquisition, transmission, and disease progression have just reported their results or will report their results in the next year. The potential impact of these interventions requires a quantitative assessment of the magnitude of the synergy between HIV and HSV-2 at the population level.

Methods and Findings

A deterministic compartmental model of HIV and HSV-2 dynamics and interactions was constructed. The nature of the epidemiologic synergy was explored qualitatively and quantitatively and compared to other sexually transmitted infections (STIs). The results suggest a more substantial role for HSV-2 in fueling HIV spread in sub-Saharan Africa than other STIs. We estimate that in settings of high HSV-2 prevalence, such as Kisumu, Kenya, more than a quarter of incident HIV infections may have been attributed directly to HSV-2. HSV-2 has also contributed considerably to the onward transmission of HIV by increasing the pool of HIV positive persons in the population and may explain one-third of the differential HIV prevalence among the cities of the Four City study. Conversely, we estimate that HIV had only a small net impact on HSV-2 prevalence.

Conclusions

HSV-2 role as a biological cofactor in HIV acquisition and transmission may have contributed substantially to HIV particularly by facilitating HIV spread among the low-risk population with stable long-term sexual partnerships. This finding suggests that prevention of HSV-2 infection through a prophylactic vaccine may be an effective intervention both in nascent epidemics with high HIV incidence in the high risk groups, and in established epidemics where a large portion of HIV transmission occurs in stable partnerships.     

Risk factors for male to female transmission of HIV. European Study Group.

OBJECTIVE--To identify risk factors for sexual transmission of HIV from infected men to their female sexual partners. DESIGN--Cross sectional analysis as part of a continuing study. Data were obtained by interviewing heterosexual couples in which the man was infected with HIV. Risks were assessed by comparing couples in which transmission had occurred (woman infected with HIV) with those in which it had not (woman not infected) and estimated by independent odds ratios and their 95% confidence intervals. SETTING--Infectious disease and public health departments from nine centres in six European countries. PARTICIPANTS--153 Male index patients (mean age 30.4 years) and their 155 female partners (mean age 27.8 years). INTERVENTIONS--Women were tested to determine their HIV antibody state. Women with a risk of infection with HIV other than sexual contact with their infected partner were excluded. END POINT--Three risk factors for male to female transmission of HIV. MEASUREMENTS AND MAIN RESULTS--Three risk factors were identified: a history of sexually transmitted disease in the previous five years for the female partner (odds ratio 3.1, 95% confidence interval 1.1 to 8.6); index patient with full blown AIDS (5.4, 1.2 to 25.2); and practice of anal intercourse (5.8, 2.3 to 14.8). The proportion of women positive for HIV antibody was 27% (42/155), ranging from 7% (1 to 13%) (4/60) for couples with none of the three risk factors to 67% (45 to 89%) (12/18) for those with two or three of the risk factors. Duration of the relationship (median three years), frequency of sexual contacts, sexual practices other than anal intercourse, and contraceptive behaviour were not associated with infection of the partner. CONCLUSIONS--The risk of sexual transmission of HIV from an infected man to his female partner varies considerably according to the characteristics of the couple. The differences in rates of transmission in high risk groups may be considerably reduced if the risk factors are taken into account during individual and public health counselling.     

Self-deception does not explain high-risk sexual behavior in the face of HIV/AIDS: A test from northern Kenya

Throughout sub-Saharan Africa, there is resistance to changing sexual behavior despite survey data indicating high levels of knowledge about HIV transmission patterns and high-risk behavior. Previous explanations for this paradox emphasize indigenous cultural models. An alternative explanation is that, due to a strong natural selection for sexual gratification, individuals evoke the evolved trait of self-deception to continue practicing high-risk sexual behavior. This alternative is tested using survey data from an Ariaal community in Marsabit District, northern Kenya. Results indicate that respondents make highly accurate self-assessments of HIV risk, negating the concept of self-deception in this study. These results are discussed within the larger context of the applicability of evolutionary theory to the AIDS pandemic.     

High Incidence Is Not High Exposure: What Proportion of Prevention Trial Participants Are Exposed to HIV?

Objective

Randomized clinical trials of HIV prevention in high-risk populations of women often assume that all participants have similar exposure to HIV. However, a substantial fraction of women enrolled in the trial may have no or low exposure to HIV. Our objective was to estimate the proportion of women exposed to HIV throughout a hypothetical high-risk study population.

Methods

A stochastic individual-based model was developed to simulate the sexual behavior and the risk of HIV acquisition for a cohort of sexually active HIV-uninfected women in high HIV prevalence settings. Key behavior and epidemic assumptions in the model were based on published studies on HIV transmission in South Africa. The prevalence of exposure, defined as the proportion of women who have sex with HIV-infected partner, and HIV incidence were evaluated.

Results

Our model projects that in communities with HIV incidence rate of 1 per 100 person years, only 5-6% of women are exposed to HIV annually while in communities with an HIV incidence of 5 per 100 person years 20-25% of women are exposed to HIV. Approximately 70% of the new infections are acquired from partners with asymptomatic HIV.

Conclusions

Mathematical models suggest that a high proportion of women enrolled in HIV prevention trials may be unexposed to HIV even when incidence rates are high. The relationship between HIV exposure and other risk factors should be carefully analyzed when future clinical trials are planned.     

Beyond Race and Place: Distal Sociological Determinants of HIV Disparities

Informed behavior change as an HIV prevention tool has yielded unequal successes across populations. Despite decades of HIV education, some individuals remain at high risk. The mainstream media often portrays these risk factors as products of race and national borders; however, a rich body of recent literature proposes a host of complex social factors that influence behavior, including, but not limited to: poverty, income inequality, stigmatizing social institutions and health care access. We examined the relationship between numerous social indicators and HIV incidence across eighty large U.S. cities in 1990 and 2000. During this time, major correlating factors included income inequality, poverty, educational attainment, residential segregation and marriage rates. However, these ecological factors were weighted differentially across risk groups (e.g. heterosexual, intravenous drug use, men who have sex with men (MSM)). Heterosexual risk rose significantly with poor economic indicators, while MSM risk depended more heavily on anti-homosexual stigma (as measured by same-sex marriage laws). HIV incidence among black individuals correlated significantly with numerous economic factors but also with segregation and imbalances in the male:female ratio (often an effect of mass incarceration). Our results support an overall model of HIV ecology where poverty, income inequality and social inequality (in the form of institutionalized racism and anti-homosexual stigma) have over time developed into synergistic drivers of disease transmission in the U.S., inhibiting information-based prevention efforts. The relative weights of these distal factors vary over time and by HIV risk group. Our testable model may be more generally applicable within the U.S. and beyond.     

The role of sexually transmitted diseases in HIV transmission

More than 42 million people worldwide are now infected with HIV, in spite of sustained prevention activities. Although the spread of HIV has been primarily sexual, epidemiological studies have indicated that the efficiency of the spread of HIV is poor, perhaps as infrequently as 1 in every 1,000 episodes of sexual intercourse. However, sexually transmitted diseases (STDs) that cause ulcers or inflammation greatly increase the efficiency of HIV transmission--by increasing both the infectiousness of, and the susceptibility to HIV infection. STDs might be particularly important in the early stages of a localized HIV epidemic, when people with risky sexual behaviour are most likely to become infected. In China, eastern Europe and Russia, there has been a remarkable increase in the incidence of STDs in recent years, and this is reflected in the rapid increase in the spread of HIV in these areas. Targeted STD detection and treatment should have a central role in HIV prevention in these emerging epidemics.     

Evidence for recent changes in sexual behaviour in homosexual men in England and Wales

Over 80% of cases of Acquired Immune Deficiency Syndrome (AIDS) in England and Wales have occurred in homosexual men. Changes in sexual behaviour in this group may have a substantial influence on the incidence of Human Immunodeficiency Virus (HIV) infection and will therefore be crucial in determining future cases of AIDS. This paper critically weighs the indirect and direct evidence for changes in behaviour in homosexual men since the advent of the AIDS epidemic. The paper reports on falling incidence of gonorrhoea, hepatitis B and syphilis in homosexual men, the changes being most marked from 1985 onwards. Data on temporal trends in HIV prevalence and incidence in homosexual men are reviewed. These suggest that the maximum incidence of HIV infection occurred in 1982-84 and may have fallen since then. Evidence for a concomitant change in sexual behaviour is reported from several sources. This points towards a recent change in sexual behaviour characterized by reduction in the numbers of partners and adoption of safer sexual practices. In some places change may have occurred as early as 1983. A change became apparent generally in 1985 and this appears to have been sustained in 1986-87. Nevertheless, a substantial proportion of homosexual men studied continue to practice high risk sexual practices, such as anal intercourse, including relationships with casual partners.