The Effect of Systemic Racism and Homophobia on Police Enforcement and Sexual and Emotional Violence among Sex Workers in East London: Findings from a Cohort Study.

There is extensive qualitative evidence of violence and enforcement impacting sex workers who are ethnically or racially minoritized, and gender or sexual minority sex workers, but there is little quantitative evidence. Baseline and follow-up data were collected among 288 sex workers of diverse genders (cis/transgender women and men and non-binary people) in London (2018-2019). Interviewer-administered and self-completed questionnaires included reports of rape, emotional violence, and (un)lawful police encounters. We used generalized estimating equation models (Stata vs 16.1) to measure associations between (i) ethnic/racial identity (Black, Asian, mixed or multiple vs White) and recent (6 months) or past police enforcement and (ii) ethnic/racial and sexual identity (lesbian, gay or bisexual (LGB) vs. heterosexual) with recent rape and emotional violence (there was insufficient data to examine the association with transgender/non-binary identities). Ethnically/racially minoritized sex workers (26.4%) reported more police encounters partly due to increased representation in street settings (51.4% vs 30.7% off-street, p = 0.002). After accounting for street setting, ethnically/racially minoritized sex workers had higher odds of recent arrest (adjusted odds ratio 2.8, 95% CI 1.3-5.8), past imprisonment (aOR 2.3, 95% CI 1.1-5.0), police extortion (aOR 3.3, 95% CI 1.4-7.8), and rape (aOR 3.6, 95% CI 1.1-11.5). LGB-identifying sex workers (55.4%) were more vulnerable to rape (aOR 2.4, 95% CI 1.1-5.2) and emotional violence. Sex workers identifying as ethnically/racially minoritized (aOR 2.1, 95% CI 1.0-4.5), LGB (aOR 2.0, 95% CI 1.0-4.0), or who use drugs (aOR 2.0, 95% CI 1.1-3.8) were more likely to have experienced emotional violence than white-identifying, heterosexual or those who did not use drugs. Experience of any recent police enforcement was associated with increased odds of rape (aOR 3.6, 95% CI 1.3-8.4) and emotional violence (aOR 4.9, 95% CI 1.8-13.0). Findings show how police enforcement disproportionately targets ethnically/racially minoritized sex workers and contributes to increased risk of rape and emotional violence, which is elevated among sexual and ethnically/racially minoritized workers.

Assortative mixing as a source of bias in epidemiological studies of sexually transmitted infections: the case of smoking and human papillomavirus.

For studies examining risk factors of sexually transmitted infections (STIs), confounding can stem from characteristics of partners of study subjects, and persist after adjustment for the subjects' individual-level characteristics. Two conditions that can result in confounding by the subjects' partners are: (C1) partner choice is assortative by the risk factor examined and, (C2) sexual activity is associated with the risk factor. The objective of this paper is to illustrate the potential impact of the assortativity bias in studies examining STI risk factors, using smoking and human papillomavirus (HPV) as an example. We developed an HPV transmission-dynamic mathematical model in which we nested a cross-sectional study assessing the smoking-HPV association. In our base case, we assumed (1) no effect of smoking on HPV, and (2) conditions C1-C2 hold for smoking (based on empirical data). The assortativity bias caused an overestimation of the odds ratio (OR) in the simulated study after perfect adjustment for the subjects' individual-level characteristics (adjusted OR 1·51 instead of 1·00). The bias was amplified by a lower basic reproductive number (R 0), greater mixing assortativity and stronger association of smoking with sexual activity. Adjustment for characteristics of partners is needed to mitigate assortativity bias.

Who mixes with whom among men who have sex with men? Implications for modelling the HIV epidemic in southern India.

In India, the identity of men who have sex with men (MSM) is closely related to the role taken in anal sex (insertive, receptive or both), but little is known about sexual mixing between identity groups. Both role segregation (taking only the insertive or receptive role) and the extent of assortative (within-group) mixing are known to affect HIV epidemic size in other settings and populations. This study explores how different possible mixing scenarios, consistent with behavioural data collected in Bangalore, south India, affect both the HIV epidemic, and the impact of a targeted intervention. Deterministic models describing HIV transmission between three MSM identity groups (mostly insertive Panthis/Bisexuals, mostly receptive Kothis/Hijras and versatile Double Deckers), were parameterised with behavioural data from Bangalore. We extended previous models of MSM role segregation to allow each of the identity groups to have both insertive and receptive acts, in differing ratios, in line with field data. The models were used to explore four different mixing scenarios ranging from assortative (maximising within-group mixing) to disassortative (minimising within-group mixing). A simple model was used to obtain insights into the relationship between the degree of within-group mixing, R0 and equilibrium HIV prevalence under different mixing scenarios. A more complex, extended version of the model was used to compare the predicted HIV prevalence trends and impact of an HIV intervention when fitted to data from Bangalore. With the simple model, mixing scenarios with increased amounts of assortative (within-group) mixing tended to give rise to a higher R0 and increased the likelihood that an epidemic would occur. When the complex model was fit to HIV prevalence data, large differences in the level of assortative mixing were seen between the fits identified using different mixing scenarios, but little difference was projected in future HIV prevalence trends. An oral pre-exposure prophylaxis (PrEP) intervention was modelled, targeted at the different identity groups. For intervention strategies targeting the receptive or receptive and versatile MSM together, the overall impact was very similar for different mixing patterns. However, for PrEP scenarios targeting insertive or versatile MSM alone, the overall impact varied considerably for different mixing scenarios; more impact was achieved with greater levels of disassortative mixing.

Differences between seven measures of self-reported numbers of clients of female sex workers in southern India: implications for individual- and population-level analysis.

Quantifying sexual activity of sub-populations with high-risk sexual behaviour is important in understanding HIV epidemiology. This study examined inconsistency of seven outcomes measuring self-reported clients per month (CPM) of female sex workers (FSWs) in southern India and implications for individual/population-level analysis. Multivariate negative binomial regression was used to compare key social/environmental factors associated with each outcome. A transmission dynamics model was used to assess the impact of differences between outcomes on population-level FSW/client HIV prevalence. Outcomes based on 'clients per last working day' produced lower estimates than those based on 'clients per typical day'. Although the outcomes were strongly correlated, their averages differed by approximately two-fold (range 39.0-79.1 CPM). The CPM measure chosen did not greatly influence standard epidemiological 'risk factor' analysis. Differences across outcomes influenced HIV prevalence predictions. Due to this uncertainty, we recommend basing population-based estimates on the range of outcomes, particularly when assessing the impact of interventions.

Men who have sex with men and women in Bangalore, South India, and potential impact on the HIV epidemic.

OBJECTIVE: The aim of this study was to quantify differences in patterns of sexual behaviour among men who have sex with men and women (MSMW) compared with men who have sex with men only (MSMO), and to examine the extent to which bisexual behaviour may act as a bridge for introducing HIV infection into the general population. METHODS: A cross-sectional survey in Bangalore city in 2006, which sampled men seeking sex with men in public places and hammams (bath houses where transgender individuals sell sex to men). RESULTS: Among a sample of 357 men reporting same-sex behaviour; 41% also reported sex with a woman in the past year and 14% were currently married to a woman, only two of whom had informed their wives about having sex with men. Condom use was very inconsistent with all male partners, while 98% reported unprotected vaginal sex with their wives. MSMW reported lower rates of risky behaviour with other men than MSMO: fewer reported selling sex (17% vs 58%), or receptive anal sex with known (28% vs 70%) or unknown (30% vs 59%) non-commercial partners. CONCLUSION: Bisexual behaviour was common among men seeking sex with men sampled in this survey. Although MSMW reported lower rates of risky sexual behaviour with male partners than MSMO, inconsistent condom use with both male and female partners indicates a potential means of HIV transmission into the general population. HIV prevention programmes and services should reach bisexual men who potentially expose their male and female partners to HIV.

Incremental role of male circumcision on a generalised HIV epidemic through its protective effect against other sexually transmitted infections: from efficacy to effectiveness to population-level impact.

BACKGROUND: Male circumcision (MC) can reduce HIV acquisition. However, a better understanding of the indirect protective effect of MC on sexually transmitted infections (STIs) is required. OBJECTIVE: To assess the incremental benefits conferred by MC on HIV infection at the individual level in circumcision trials (no herd immunity effect) and at the population level (with herd immunity effect) owing to its protective effect against other STIs. METHODS: A dynamic stochastic model of HIV and STI infections in a Kenyan population was used to simulate the impact of MC offered to a few trial participants or to a large proportion of men in order to study the protective role of MC on HIV infection at the individual and population levels. RESULTS: Fewer than 20% of the HIV infections prevented in the circumcised arm of the circumcision trials (individual level) could be attributable to the efficacy of MC against STIs rather than against HIV. At the population level, MC can significantly reduce the prevalence of HIV, especially among men and women in the longer term. However, even at the population level, the long-term incremental impact of MC on HIV due to the protection against STI is modest (even if MC efficacy against the STI and STI prevalence was high). CONCLUSIONS: The protection of MC against STI contributes little to the overall effect of MC on HIV. Additional work is needed to determine whether, and under what conditions, the protective effect of MC efficacy against STIs can have a significant incremental benefit on the HIV epidemic.

Evaluating large-scale HIV prevention interventions: study design for an integrated mathematical modelling approach.

BACKGROUND: There is an urgent need to evaluate HIV prevention interventions, thereby improving our understanding of what works, under what circumstances and what is cost effective. OBJECTIVES: To describe an integrated mathematical evaluation framework designed to assess the population-level impact of large-scale HIV interventions and applied in the context of Avahan, the Indian AIDS Initiative, in southern India. The Avahan Initiative is a large-scale HIV prevention intervention, funded by the Bill & Melinda Gates Foundation, which targets high-risk groups in selected districts of the six states most affected by the HIV/AIDS epidemic (Maharashtra, Karnataka, Tamil Nadu, Andhra Pradesh, Nagaland and Manipur) and along the national highways. METHODS: One important component of the monitoring and evaluation of Avahan relies on an integrated mathematical framework that combines empirical biological and behavioural data from different subpopulations in the intervention areas, with the use of tailor-made transmission dynamics models embedded within a Bayesian framework. RESULTS: An overview of the Avahan Initiative and the objectives of the monitoring and evaluation of the intervention is given. The rationale for choosing this evaluation design compared with other possible designs is presented, and the different components of the evaluation framework are described and its advantages and challenges are discussed, with illustrated examples. CONCLUSIONS: This is the first time such an approach has been applied on such a large scale. Lessons learnt from the CHARME project could help in the design of future evaluations of large-scale interventions in other settings, whereas the results of the evaluation will be of programmatic and public health relevance.

A Bayesian approach to estimate changes in condom use from limited human immunodeficiency virus prevalence data.

Evaluation of large-scale intervention programmes against human immunodeficiency virus (HIV) is becoming increasingly important, but impact estimates frequently hinge on knowledge of changes in behaviour such as the frequency of condom use over time, or other self-reported behaviour changes, for which we generally have limited or potentially biased data. We employ a Bayesian inference methodology that incorporates an HIV transmission dynamics model to estimate condom use time trends from HIV prevalence data. Estimation is implemented via particle Markov chain Monte Carlo methods, applied for the first time in this context. The preliminary choice of the formulation for the time varying parameter reflecting the proportion of condom use is critical in the context studied, because of the very limited amount of condom use and HIV data available. We consider various novel formulations to explore the trajectory of condom use over time, based on diffusion-driven trajectories and smooth sigmoid curves. Numerical simulations indicate that informative results can be obtained regarding the amplitude of the increase in condom use during an intervention, with good levels of sensitivity and specificity performance in effectively detecting changes. The application of this method to a real life problem demonstrates how it can help in evaluating HIV interventions based on a small number of prevalence estimates, and it opens the way to similar applications in different contexts.

Complementary hypothesis concerning the community sexually transmitted disease mass treatment puzzle in Rakai, Uganda.

OBJECTIVES: To study the dynamics of a mass treatment programme for sexually transmitted diseases (STD) on prevalence of STD and HIV incidence in order to help explain the results of the STD mass treatment community trial in Rakai, Uganda. METHODS: The analysis is based on simulations of STD mass treatment interventions using a deterministic model describing the course of STD and HIV transmission over time and incorporating demographic, biological and behavioural parameters. The mass intervention modelled mimics that used in the Rakai community trial. RESULTS: Mass treatment decreases STD prevalence to a very low level compared with baseline but is unsuccessful at eradicating the infection. STD prevalences return to baseline fairly rapidly after each round of mass treatment. Under different realistic scenarios, the fraction of HIV cases prevented by STD mass treatment assuming uniform 80% coverage of high- and low-risk groups, over the 20-month period following the first round of treatment, was greater than 35%. If, however, differential coverage is assumed, for example that while the total coverage is still 80%, only 40 or 25% of those at high risk are treated, the HIV preventable fraction is reduced, to 19 and 15% respectively (undetectable given the statistical power of the study). The tremendous impact of differential coverage can also be observed even in the early stage of the HIV epidemic. CONCLUSIONS: In the Rakai trial, mass treatment may have had an effect, although transient, on all STD prevalences, which could have had positive repercussions for HIV incidence. This modelling exercise suggests that although an 80% coverage appears high, the differential coverage of low- and high-risk populations may seriously impair our ability to test the STD-HIV interaction hypothesis.

The influence of different sexual-contact patterns between age classes on the predicted demographic impact of AIDS in developing countries.

A model is developed to describe the spread of HIV within heterosexual communities and the demographic impact of AIDS. The model combines epidemiologic and demographic processes and is designed to mirror the impact of AIDS in sub-Saharan Africa. Refinements on past work in this area include unequal probabilities for transmission from females to males and from males to females, the inclusion of an age- and sex-dependent sexual-partner choice function and distributed incubation plus infectious periods. Numerical studies suggest that unequal transmission probabilities (weighted to a greater probability from males to females than vice versa), and the tendency of males to choose sexual partners of the opposite sex younger than themselves, both act to increase the demographic impact of AIDS over that predicted with equal transmission between the sexes and partner choice restricted within given age classes. Analyses support the conclusions of past work that the epidemic will only have a small detrimental impact on the dependency ratio of a population (the ratio of dependents to working adults) even when a weighting is added to take account of the extra burden imposed by the care of adult AIDS patients. However, a small increase in the ratio can imply a significant rise in the number of dependents within the population. Stimulation studies of the impact of changes in behavior to reduce transmission highlight to the need to induce such changes as early as possible in the course of the epidemic in order to minimize its impact. Directions for future research are discussed emphasizing the need to acquire quantitative data on sexual habits and to construct models to represent heterogeneity in sexual behavior.

PIP: A mathematical model of the likely demographic impact of acquired immunodeficiency syndrome (AIDS) suggest that, in the countries of sub- Saharan Africa, this impact can be expected to increase in the years ahead as a result of unequal transmission probabilities (weighted toward a greater probability from males to females) and the tendency of men to select female sexual partners from a younger class. The model refines earlier work in its consideration of predicted influence of human immunodeficiency virus (HIV) infection on the age structure and dependency ratio of the population, the significance of patterns of sexual contact between the age classes of the 2 sexes, and the impact of control measures such as health education and condom use. The assumptions of a doubling time of 1.5 years in the early stages of the epidemic and a 3 times greater probability of transmission from infected males to susceptible females rather than vice versa produce the observation that net population growth rate will change from positive to negative 25 years after introduction of the AIDS virus. The dependency ration is not significantly affected by AIDS due to the counterbalancing effects of deaths from vertical and horizontal transmission. On the other hand, if dependency ratio is defined to encompass the burden created by the care of AIDS patients, the disease-related ratio will increase over time. The most significant social factor in terms of the impact of AIDS on net fertility is the tendency of African men to choose female sexual partners at least 5 years younger than themselves. Finally, the numerical analyses indicate that the introduction of AIDS control measures 10 years after the onset of the epidemic will slow the progression of the epidemic and prevent a change in the population growth rate from positive to negative over a 100-year period.

The impact of HIV and other STDs on human populations. Are predictions possible?

This article presents an overview of the use of mathematical models to study the demographic impact of STDs. Written for the nonmathematician, the article introduces the basic concepts of mathematical epidemiology for infectious diseases, such as the mass-action principle, the threshold density concept, and the basic reproductive rate. Described are the main features that characterize the epidemiology of STDs and those features that differentiate them from other directly transmitted diseases, such as measles, rubella, and others. Also presented are major findings concerning the importance of sexual behavior on the dynamics of STD transmission, and the numerical analysis of the demographic impact on gonococcal and HIV infections using a mathematical model. The epidemiology of these two STDs is explored, as well as how the growth rate of the population can influence the epidemiology of these STDs. Finally, the authors demonstrate how, under some circumstances, early treatment of gonorrhea can reduce the demographic impact of HIV in regions most affected by both diseases.

Mathematical models of disease transmission: a precious tool for the study of sexually transmitted diseases.

This paper is an introduction to the mathematical epidemiology of sexually transmitted diseases (STDs) and its application to public health. After a brief introduction to transmission dynamics models, the construction of a deterministic compartmental mathematical model of HIV transmission in a population is described. As a background to STD transmission dynamics, basic reproductive rate, intergroup mixing, rate of partner change, and duration of infectivity are discussed. Use of the models illustrates the effect of sexual mixing (proportionate to highly assortative), of preventive intervention campaigns, and of HIV-chlamydia interaction on HIV prevalence in the different population groups. In particular, planned prevention campaigns can benefit the targeted intervention group but surprisingly can be disadvantageous for the general population. Through examples, mathematical models are shown to be helpful in our understanding of disease transmission, in interpretation of observed trends, in planning of prevention strategies, and in guiding data collection.

Sexual identity and its contribution to MSM risk behavior in Bangaluru (Bangalore), India: the results of a two-stage cluster sampling survey.

In India, there are categories of MSM (hijras, kothis, double-deckers, panthis and bisexuals), which are generally associated with different HIV-risk behaviors. Our objective was to quantify differences across MSM identities (n = 357) and assess the extent they conform to typecasts that prevail in policy-orientated discourse. More feminine kothis (26%) and hijras (13%) mostly reported receptive sex, and masculine panthis (15%) and bisexuals (23%) insertive anal sex. However, behavior did not always conform to expectation, with 25% and 16% of the sample reporting both insertive and receptive anal intercourse with known and unknown noncommercial partners, respectively (p < 0.000). Although behavior often complied with stereotyped role and identity, male-with-male sexual practices were fluid. Reification of these categories in an intervention context may hinder our understanding of the differential HIV risk among MSM.

What is the achievable effectiveness of the India AIDS Initiative intervention among female sex workers under target coverage? Model projections from southern India.

BACKGROUND: The India AIDS Initiative (Avahan) prevention programme funded by the Bill and Melinda Gates Foundation aims to reduce HIV prevalence in high risk groups such as female and male sex workers and their clients, to limit HIV transmission in the general population. OBJECTIVES: To assess the potential effectiveness of the Avahan intervention at the level of coverage targeted, in different epidemiological settings in India. METHODS: A deterministic compartmental model of the transmission dynamics of HIV and two sexually transmitted infections, and sensitivity analysis techniques, were used, in combination with available behavioural and epidemiological data from Mysore and Bagalkot districts in the Indian state of Karnataka, to evaluate the syndromic sexually transmitted infection (STI) management (STI treatment), periodic presumptive treatment of STI (PPT), and condom components of the Avahan intervention targeted to female sex workers (FSW). RESULTS: If all components of the intervention reach target coverage (that is, PPT, STI treatment and condom use), the intervention is expected to prevent 22-35% of all new HIV infections in FSW and in the total population over 5 years in a low transmission setting like Mysore, and to be half as effective in high transmission settings such as Bagalkot. The results were sensitive to small variations in intervention coverage. The condom component alone is expected to prevent around 20% of all new HIV infections over 5 years in Mysore and around 6% for the STI component alone; compared with 7%-14% for the PPT component alone. Multivariate sensitivity analyses suggested that interventions may be more effective in settings with low FSW HIV prevalence and small FSW populations, whereas HIV prevalence was most influenced by sexual behaviour and condom use parameters for FSW. CONCLUSION: The Avahan intervention is expected to be effective. However, to be able to demonstrate effectiveness empirically in the different settings, it is important to achieve target coverage or higher, which in the case of PPT could take a number of years to achieve. These preliminary model predictions need to be validated with more detailed mathematical models, as better data on sexual behaviour, condom use, STI and HIV trends over time, and intervention coverage data accumulate over the course of the programme.

Sexual contact patterns between men and women and the spread of HIV-1 in urban centres in Africa.

A simple model of the transmission of HIV-1 by heterosexual contact and from mother to unborn infant is developed to assess the influence of patterns of mixing between low and high sexual activity classes of the two sexes on the pattern of spread of the virus and the demographic impact of AIDS. Numerical studies of model behaviour are based, where possible, on parameter estimates derived from epidemiological studies of HIV-1 spread in Africa. Analyses reveal that the assumed pattern of mixing, ranging from assortative (like with like) through random (proportional) to disassortative (like with unlike), has a very major impact on the predicted spread of the virus and the concomitant demographic impact of AIDS. Patterns of strong assortative mixing are predicted to generate the least spread and demographic impact, by comparison with proportional or disassortative mixing. Analyses also reveal that the rules governing behaviour changes, once AIDS-induced mortality changes the structure of the population (i.e. the numbers in the low and high sexual activity classes of the two sexes), have a very significant influence on the course of the epidemic. Where possible, predicted patterns are compared with observed trends in Africa.

Human immunodeficiency virus transmission and the role of other sexually transmitted diseases. Measures of association and study design.

BACKGROUND: Studies have reported that infection with certain sexually transmitted diseases (STD), such as chancroid, gonorrhea, and genital herpes, enhances the probability of human immunodeficiency virus (HIV) transmission by sexual contact with an infected partner. Epidemiologic studies vary in design from longitudinal to cross-sectional, with varying periods of follow-up or retrospective history of exposure to STD. The major difficulty in assessing the results of past work centers on the validity and precision of widely used measures of association, such as relative risk (RR) and odds ratio (OR), in situations in which common behavior (e.g., different facets of sexual behavior) underpins the acquisition of both the STD cofactor and HIV. GOAL: To evaluate the quality of the cumulative incidence ratio (CIR), the hazard rate ratio (HRR), and the prevalence ratio (PR) as measures of association to estimate and test the increase in HIV transmission probabilities caused by the STD. STUDY DESIGN: The study is based on a proportional hazard stochastic model of concomitant HIV and STD cofactor transmission. Analysis was performed using Monte-Carlo simulation. RESULTS: Estimates of the HIV-STD association by the CIR, HRR, and PR, adjusted and nonadjusted for sexual activity, are shown to have poor validity and great variability. The adjusted CIR, HRR, and PR tend to underestimate the strength of the true association (specified in the model) in both longitudinal and cross-sectional designs. In the absence an HIV-STD association, the PR tends to overestimate the magnitude, whereas the CIR and HRR may either underestimate or overestimate it in longitudinal studies. These results have direct consequences on the reliability of the test of association showing both a lack of specificity (empirical type I error) and sensitivity (empirical power). Some reasons contributing to the bias in the estimates of the measures of association are the presence of confounding variables, namely the frequency of change of sex partner and the mixing pattern between sexual activity classes, as well as the adopted definition of exposure to the STD cofactor and the prevalence of both HIV and the STD cofactor. CONCLUSIONS: The precision of estimates and reliability of the test of HIV-STD association could be improved through longitudinal studies using more careful definition and measurement of exposure to the STD cofactor and larger sample sizes permitting finer stratification of sexual behavior and a sufficient number of persons per stratum.

The impact of HIV epidemic phases on the effectiveness of core group interventions: insights from mathematical models.

Mathematical models have highlighted the disproportionate contribution of core group transmitters to the spread of sexually transmitted diseases. Because the effectiveness of interventions varies with time, it has been suggested that epidemic phases should be considered in the design of prevention strategies. This study aimed to examine the impact of HIV epidemic phases on the effectiveness of HIV interventions based on gonorrhoea screening and condom use, targeted to core groups. The results are based on a mathematical model of gonorrhoea and HIV transmission in a relatively slow spreading HIV epidemic using Cotonou (Benin) as an example. For epidemics with a low reproductive potential modest core group interventions can significantly reduce HIV incidence and prevalence. As the epidemic matures, effective interventions should also incorporate core and non-core populations. For epidemics with a high reproductive potential, core group interventions are necessary but not sufficient to have a rapid and large scale impact. A more general population approach is also needed early in the epidemic. Epidemic phases are also important in the evaluation of prevention strategies.

Slowing the spread of human immunodeficiency virus in developing countries.

PIP: This article assesses the current status of the AIDS epidemic and discusses interventions and policies needed to control the spread of the disease. The authors explain that the lack of effective therapies and vaccines makes changing human behavior and introducing preventive measures all the more crucial. In some areas of sub-Saharan Africa, the epidemic has reached alarming proportions, with up to 1/10 to 1/3 of all sexually active adults carrying the AIDS virus. Epidemiological studies indicate that throughout Africa, the doubling time of the disease is 1-5 years, the female prostitutes constitute one of the main transmission routes, and the condom use does slow the transmission of HIV. Mathematical model reveal the benefits of early intervention strategies aimed at high-risk groups, and highlight the need to alter the sexual contact patterns between high-risk and low-risk groups. Some of the intervention strategies suggested by the article include: implementing HIV and AIDs education programs; encouraging fewer sexual partners and more safe-sex practices; reinforcing messages through multiple communications channels; promoting condom distribution, improving diagnosis and treatment programs; and improving drug abuse treatment programs and access to clean needles. The authors discuss the cost, time factors, bureaucratic obstacles, and effectiveness of these measures. Concerning policy, the authors list some of the issues that need to be addressed. These include the need to focus resources according to the prevalence of HIV; the need for multiple intervention strategies; the need for early and well-funded programs; the need to take into consideration the impact of population growth on the spread of the virus; and the need to care for AIDS-stricken patients.^ieng

Some methodological issues in the study of sexual networks: from model to data to model.

BACKGROUND: Mixing between sexual activity classes is an important determinant of sexually transmitted disease transmission. However, attempts to estimate sexual mixing patterns in the field remain limited partly because of practical and methodological difficulties. GOAL: To evaluate and identify appropriate sampling schemes to estimate the mixing pattern between sexual activity classes from large population networks with one or more components. STUDY DESIGN: The study is based on simulations of large population networks with various structural characteristics. A variety of snowball sampling schemes are applied to these networks and are evaluated by the quality of the mixing matrix estimates that they produce. RESULTS AND CONCLUSIONS: Unbiased estimation of mixing patterns (global assortativity, within-group mixing of the lowest activity classes, within-group mixing of the highest activity classes) from large population networks is possible with a snowball sampling design in which the initial sample of index cases is drawn from the general population, all partners of the index case are recruited, and only one generation of partners are traced (one cycle). Simulation techniques proved useful in addressing complex methodological issues in situations where analytic results are difficult to obtain.