Modelling sexual transmission of HIV: testing the assumptions, validating the predictions

Challenges and Opportunities in Big Data Science to Address Health Inequities and Focus the HIV Response

PURPOSE OF REVIEW

Big Data Science can be used to pragmatically guide the allocation of resources within the context of national HIV programs and inform priorities for intervention. In this review, we discuss the importance of grounding Big Data Science in the principles of equity and social justice to optimize the efficiency and effectiveness of the global HIV response.

RECENT FINDINGS

Social, ethical, and legal considerations of Big Data Science have been identified in the context of HIV research. However, efforts to mitigate these challenges have been limited. Consequences include disciplinary silos within the field of HIV, a lack of meaningful engagement and ownership with and by communities, and potential misinterpretation or misappropriation of analyses that could further exacerbate health inequities. Big Data Science can support the HIV response by helping to identify gaps in previously undiscovered or understudied pathways to HIV acquisition and onward transmission, including the consequences for health outcomes and associated comorbidities. However, in the absence of a guiding framework for equity, alongside meaningful collaboration with communities through balanced partnerships, a reliance on big data could continue to reinforce inequities within and across marginalized populations.

Infectious Disease Modelling of HIV Prevention Interventions: A Systematic Review and Narrative Synthesis of Compartmental Models

BACKGROUND

The HIV epidemic remains a major public health problem. Critical to transmission control are HIV prevention strategies with new interventions continuing to be developed. Mathematical models are important for understanding the potential impact of these interventions and supporting policy decisions. This systematic review aims to answer the following question: when a new HIV prevention intervention is being considered or designed, what information regarding it is necessary to include in a compartmental model to provide useful insights to policy makers? The primary objective of this review is therefore to assess suitability of current compartmental HIV prevention models for informing policy development.

METHODS

Articles published in EMBASE, Medline, Econlit, and Global Health were screened. Included studies were identified using permutations of (i) HIV, (ii) pre-exposure prophylaxis (PrEP), circumcision (both voluntary male circumcision [VMMC] and early-infant male circumcision [EIMC]), and vaccination, and (iii) modelling. Data extraction focused on study design, model structure, and intervention incorporation into models. Article quality was assessed using the TRACE (TRAnsparent and Comprehensive Ecological modelling documentation) criteria for mathematical models.

RESULTS

Of 837 articles screened, 48 articles were included in the review, with 32 unique mathematical models identified. The substantial majority of studies included PrEP (83%), whilst fewer modelled circumcision (54%), and only a few focussed on vaccination (10%). Data evaluation, implementation verification, and model output corroboration were identified as areas of poorer model quality. Parameters commonly included in the mathematical models were intervention uptake and effectiveness, with additional intervention-specific common parameters identified. We identified key modelling gaps; critically, models insufficiently incorporate multiple interventions acting simultaneously. Additionally, population subgroups were generally poorly represented-with future models requiring improved incorporation of ethnicity and sexual risk group stratification-and many models contained inappropriate data in parameterisation which will affect output accuracy.

CONCLUSIONS

This review identified gaps in compartmental models to date and suggests areas of improvement for models focusing on new prevention interventions. Resolution of such gaps within future models will ensure greater robustness and transparency, and enable more accurate assessment of the impact that new interventions may have, thereby providing more meaningful guidance to policy makers.

The impact of condom use on the HIV epidemic

Background: Condom promotion and supply was one the earliest interventions to be mobilized to address the HIV pandemic. Condoms are inexpensive and provide protection against transmission of HIV and other sexually transmitted diseases (STIs) as well as against unintended pregnancy. As many as 16 billion condoms may be used annually in all low- and middle-income countries (LMIC). In recent years the focus of HIV programs as been on testing and treatment and new technologies such as PrEP. Rates of condom use have stopped increasing short of UNAIDS targets and funding from donors is declining. Methods: We applied a mathematical HIV transmission model to 77 high HIV burden countries to estimate the number of HIV infections that would have occurred from 1990 to 2019 if condom use had remained at 1990 levels. Results: The results suggest that current levels of HIV would be five times higher without condom use and that the scale-up in condoms use averted about 117 million HIV infections. Conclusions: HIV programs should ensure that affordable condoms are consistently available and that the benefits of condom use are widely understood.

The impact of condom use on the HIV epidemic

Background: Condom promotion and supply was one the earliest interventions to be mobilized to address the HIV pandemic. Condoms are inexpensive and provide protection against transmission of HIV and other sexually transmitted diseases (STIs) as well as against unintended pregnancy. As many as 16 billion condoms may be used annually in all low- and middle-income countries (LMIC). In recent years the focus of HIV programs as been on testing and treatment and new technologies such as PrEP. Rates of condom use have stopped increasing short of UNAIDS targets and funding from donors is declining. Methods: We applied a mathematical HIV transmission model to 77 high HIV burden countries to estimate the number of HIV infections that would have occurred from 1990 to 2019 if condom use had remained at 1990 levels. Results: The results suggest that current levels of HIV would be five times higher without condom use and that the scale-up in condoms use averted about 117 million HIV infections. Conclusions: HIV programs should ensure that affordable condoms are consistently available and that the benefits of condom use are widely understood.

Cost analysis of treatment strategies for the control of HSV-2 infection in the U.S.: A mathematical modeling-based case study

Infection of Herpes Simplex Virus type 2 (HSV-2) is a lifelong sexually transmitted disease. According to the Center for Disease Control and Prevention (CDC), 11.9% of the United States (U.S.) population was infected with HSV-2 in 2015-2016. The HSV-2 pathogen establishes latent infections in neural cells and can reactivate causing lesions later in life, a strategy that increases pathogenicity and allows the virus to evade the immune system. HSV-2 infections are currently treated by Acyclovir only in the non-constitutional stage, marked by genital skin lesions and ulcers. However, patients in the constitutional stage expressing mild and common (with other diseases) symptoms, such as fever, itching and painful urination, remain difficult to detect and are untreated. In this study, we develop and analyze a mathematical model to study the transmission and control of HSV-2 among the U.S. population between the ages of 15-49 when there are options to treat individuals in different stages of their pathogenicity. In particular, the goals of this work are to study the effect on HSV-2 transmission dynamics and to evaluate and compare the cost-effectiveness of treating HSV-2 infections in both constitutional and non-constitutional stages (new strategy) against the current conventional treatment protocol for treating patients in the non-constitutional stage (current strategy). Our results distinguish model parameter regimes where each of the two treatment strategies can optimize the available resources and consequently gives the long-term reduced cost associated with each treatment and incidence. Moreover, we estimated that the public health cost of HSV-2 with the proposed most cost-effective treatment strategy would increase by approximately 1.63% in 4 years of implementation. However, in the same duration, early treatment via the new strategy will reduce HSV-2 incidence by 42.76% yearly and the reproduction number will decrease to 0.84 from its current estimate of 2.5. Thus, the proposed new strategy will be significantly cost-effective in controlling the transmission of HSV-2 if the strategy is properly implemented.

Mortality in the First 3 Months on Antiretroviral Therapy Among HIV-Positive Adults in Low- and Middle-income Countries: A Meta-analysis

Previous meta-analyses reported mortality estimates of 12-month post-antiretroviral therapy (ART) initiation; however, 40%-60% of deaths occur in the first 3 months on ART, a more sensitive measure of averted deaths through early ART initiation. To determine whether early mortality is dropping as treatment thresholds have increased, we reviewed studies of 3 months on ART initiation in low- to middle-income countries. Studies of 3-month mortality from January 2003 to April 2016 were searched in 5 databases. Articles were included that reported 3-month mortality from a low- to middle-income country; nontrial setting and participants were ≥15. We assessed overall mortality and stratified by year using random effects models. Among 58 included studies, although not significant, pooled estimates show a decline in mortality when comparing studies whose enrollment of patients ended before 2010 (7.0%; 95% CI: 6.0 to 8.0) with the studies during or after 2010 (4.0%; 95% CI: 3.0 to 5.0). To continue to reduce early HIV-related mortality at the population level, intensified efforts to increase demand for ART through active testing and facilitated referral should be a priority. Continued financial investments by multinational partners and the implementation of creative interventions to mitigate multidimensional complex barriers of accessing care and treatment for HIV are needed.

Reproductive justice & preventable deaths: state funding, family planning, abortion, and infant mortality, US 1980-2010

INTRODUCTION

Little current research examines associations between infant mortality and US states' funding for family planning services and for abortion, despite growing efforts to restrict reproductive rights and services and documented associations between unintended pregnancy and infant mortality.

MATERIAL AND METHODS

We obtained publicly available data on state-only public funding for family planning and abortion services (years available: 1980, 1987, 1994, 2001, 2006, and 2010) and corresponding annual data on US county infant death rates. We modeled the funding as both fraction of state expenditures and per capita spending (per woman, age 15-44). State-level covariates comprised: Title X and Medicaid per capita funding, fertility rate, and percent of counties with no abortion services; county-level covariates were: median family income, and percent: black infants, adults without a high school education, urban, and female labor force participation. We used Possion log-linear models for: (1) repeat cross-sectional analyses, with random state and county effects; and (2) panel analysis, with fixed state effects.

RESULTS

Four findings were robust to analytic approach. First, since 2000, the rate ratio for infant death comparing states in the top funding quartile vs. no funding for abortion services ranged (in models including all covariates) between 0.94 to 0.98 (95% confidence intervals excluding 1, except for the 2001 cross-sectional analysis, whose upper bound equaled 1), yielding an average 15% reduction in risk (range: 8 to 22%). Second, a similar risk reduction for state per capita funding for family planning services occurred in 1994. Third, the excess risk associated with lower county income increased over time, and fourth, remained persistently high for counties with a high percent of black infants.

CONCLUSIONS

Insofar as reducing infant mortality is a government priority, our data underscore the need, despite heightened contention, for adequate public funding for abortion services and for redressing health inequities.

Acute HIV infection transmission among people who inject drugs in a mature epidemic setting

OBJECTIVE

Estimates for the contribution of transmission arising from acute HIV infections (AHIs) to overall HIV incidence vary significantly. Furthermore, little is known about AHI-attributable transmission among people who inject drugs (PWID), including the extent to which interventions targeting chronic infections (e.g. HAART as prevention) are limited by AHI transmission. Thus, we estimated the proportion of transmission events attributable to AHI within the mature HIV epidemic among PWID in New York City (NYC).

DESIGN

Modeling study.

METHODS

We constructed an interactive sexual and injecting transmission network using an agent-based model simulating the HIV epidemic in NYC between 1996 and 2012. Using stochastic microsimulations, we cataloged transmission from PWID based on the disease stage of index agents to determine the proportion of infections transmitted during AHI (in primary analyses, assumed to last 3 months).

RESULTS

Our calibrated model approximated the epidemiological features of the mature HIV epidemic in NYC between 1996 and 2012. Annual HIV incidence among PWID dropped from approximately 1.8% in 1996 to 0.7% in 2012. Over the 16-year period, AHI accounted for 4.9% (10th/90th percentile: 0.1-12.3%) of incident HIV cases among PWID. The annualized contribution of AHI increased over this period from 3.6% in 1996 to 5.9% in 2012.

CONCLUSION

Our results suggest that, in mature epidemics such as NYC, between 3% and 6% of transmission events are attributable to AHI among PWID. Current HIV treatment as prevention strategies are unlikely to be substantially affected by AHI-attributable transmission among PWID populations in mature epidemic settings.

How do HIV-negative individuals in sub-Saharan Africa change their sexual risk behaviour upon learning their serostatus? A systematic review

OBJECTIVE

To determine whether, and how, sexual behaviour of HIV-negative individuals in sub-Saharan Africa (SSA) changes upon learning their serostatus.

METHODS

We systematically reviewed the published literature using EMBASE and Medline to search for publications between 2004 and 2014. We included studies that quantified behaviour change (condom use, number of sexual partners or sex acts) following an HIV test in HIV-negative adults in SSA, and extracted relevant data including study characteristics and measurement type.

RESULTS

From 2185 unique citations, n=14 studies representing 22 390 participants met our inclusion criteria. We did not pool data due to marked heterogeneity in study outcome measures. The proportion of participants reporting consistent condom use (n=6) post-testing ranged from 7.6% greater, to 10.6% fewer, while 'no condom use' (n=5) ranged from 40.0% less, to 0.7% more. Condom use in serodiscordant couples increased (n=3). Five studies measured the proportion reporting abstinence, finding an increase of 10.9% to a decrease of 5.3% post-testing. The post-testing change in the mean number of sex acts (n=3) ranged from a relative decrease of 15.7% to a relative increase of 9.4%. Two studies reported relative decreases in the mean number of sexual partners of 35.2% and 14.0%. Three studies examining serodiscordant primary relationships specifically all showed increases in extrarelational sex.

CONCLUSIONS

With the exception of serodiscordant couples, there is variable evidence that awareness of one's serostatus leads to substantial changes in risk behaviour among HIV-negative individuals. Further research is needed to estimate the behavioural impact of learning one's serostatus in SSA.

Critical considerations for adopting the HIV 'treat all' approach in Zimbabwe: is the nation poised?

While the advent of antiretroviral therapy (ART) has increased survival and reduced the number of acquired immune-deficiency syndrome (AIDS) related deaths among people living with the human immunodeficiency virus (HIV) virus (PLHIV), HIV/AIDS remains a global health problem and sub-Saharan Africa continues to bear the greatest burden of disease. There are also major challenges in the HIV response: as of December 2013, only 36% of PLHIV globally were on ART, and for every individual started on ART there were two new PLHIV diagnosed. This has led to considerable debate around adopting an HIV 'treat all' approach aimed at greatly escalating the number of PLHIV initiated and retained on ART, regardless of CD4 cell count or World Health Organization (WHO) clinical stage, with the intended goal of achieving viral suppression which should in turn reduce HIV transmission, morbidity and mortality in affected individuals. This paper examines the issues being discussed in Zimbabwe, a low-income country with a high burden of HIV/AIDS, about the implications and opportunities of adopting an HIV 'treat all' approach, along with pertinent operational research questions that need to be answered to move the agenda forward. These discussions are timely, given the recent WHO recommendations advising ART for all PLHIV, regardless of CD4 cell count.

Reconceptualizing the HIV epidemiology and prevention needs of Female Sex Workers (FSW) in Swaziland

BACKGROUND

HIV is hyperendemic in Swaziland with a prevalence of over 25% among those between the ages of 15 and 49 years old. The HIV response in Swaziland has traditionally focused on decreasing HIV acquisition and transmission risks in the general population through interventions such as male circumcision, increasing treatment uptake and adherence, and risk-reduction counseling. There is emerging data from Southern Africa that key populations such as female sex workers (FSW) carry a disproportionate burden of HIV even in generalized epidemics such as Swaziland. The burden of HIV and prevention needs among FSW remains unstudied in Swaziland.

METHODS

A respondent-driven-sampling survey was completed between August-October, 2011 of 328 FSW in Swaziland. Each participant completed a structured survey instrument and biological HIV and syphilis testing according to Swazi Guidelines.

RESULTS

Unadjusted HIV prevalence was 70.3% (n = 223/317) among a sample of women predominantly from Swaziland (95.2%, n = 300/316) with a mean age of 21(median 25) which was significantly higher than the general population of women. Approximately one-half of the FSW(53.4%, n = 167/313) had received HIV prevention information related to sex work in the previous year, and about one-in-ten had been part of a previous research project(n = 38/313). Rape was common with nearly 40% (n = 123/314) reporting at least one rape; 17.4% (n = 23/314)reported being raped 6 or more times. Reporting blackmail (34.8%, n = 113/314) and torture(53.2%, n = 173/314) was prevalent.

CONCLUSIONS

While Swaziland has a highly generalized HIV epidemic, reconceptualizing the needs of key populations such as FSW suggests that these women represent a distinct population with specific vulnerabilities and a high burden of HIV compared to other women. These women are understudied and underserved resulting in a limited characterization of their HIV prevention, treatment, and care needs and only sparse specific and competent programming. FSW are an important population for further investigation and rapid scale-up of combination HIV prevention including biomedical, behavioral, and structural interventions.

Conceptual framework and research methods for migration and HIV transmission dynamics

Migration and mobility have had a profound influence on the global HIV epidemic. We propose a network-dyadic conceptual model to interpret previous literature and inform the development of future research with respect to study design, measurement methods, and analytic approach. In this model, HIV transmission is driven by risk behaviors of migrants that emerges and is enabled by mobility, the bridging of sub-epidemics across space and time, and the displacement effects on the primary residential sending community for migrants. To investigate these causal pathways, empirical study designs must measure the relative timing of migratory events, sexual risk behaviors, and incident HIV infections. Network-based mathematical models using empirical data on partnerships help gain insight into the dynamic disease transmission systems. Although the network-dyadic conceptual model and related network methods may not address all questions related to migration and HIV, they provide a unified approach for future research on this important topic.

Assessing the cost effectiveness of pre-exposure prophylaxis for HIV prevention in the US

About 50,000 people are infected with HIV in the US each year and this number has remained virtually the same for the past decade. Yet, in the last few years, evidence from several multinational randomized clinical trials has shown that the provision of antiretroviral drug to uninfected persons (i.e. pre-exposure prophylaxis) reduces the incidence of HIV by about 50 %. However, evidence from cost-effectiveness studies conducted in the US yield widely varying estimates of the cost per quality-adjusted life-year (QALY) gained, and this variation reflects the substantial uncertainty surrounding the determinants of HIV transmission (e.g. adherence rates to prophylactic medications, the average number of sexual partners, the number and types of sexual acts, the viral load of infected partners, and the proportion of contacts where condoms are used), as well as different approaches to translating a reduction in HIV cases into an estimate of the increase in the number of QALYs.

Clinical uncertainties, health service challenges, and ethical complexities of HIV "test-and-treat": a systematic review

Despite the HIV "test-and-treat" strategy's promise, questions about its clinical rationale, operational feasibility, and ethical appropriateness have led to vigorous debate in the global HIV community. We performed a systematic review of the literature published between January 2009 and May 2012 using PubMed, SCOPUS, Global Health, Web of Science, BIOSIS, Cochrane CENTRAL, EBSCO Africa-Wide Information, and EBSCO CINAHL Plus databases to summarize clinical uncertainties, health service challenges, and ethical complexities that may affect the test-and-treat strategy's success. A thoughtful approach to research and implementation to address clinical and health service questions and meaningful community engagement regarding ethical complexities may bring us closer to safe, feasible, and effective test-and-treat implementation.

Cost-effectiveness of pre-exposure prophylaxis for HIV: a review

PURPOSE OF REVIEW

The US Food and Drug Administration (FDA) recently approved the use of tenofovir-emtricitabine for pre-exposure prophylaxis (PrEP) for HIV prevention. PrEP is also being investigated in clinical trials as a component of HIV prevention in resource-limited settings. Cost-effectiveness models are useful in identifying health programs with the greatest societal value and projecting long-term program impacts. This review examines six recent studies of the cost-effectiveness of PrEP for preventing HIV transmission in the USA and South Africa.

RECENT FINDINGS

Studies used both individual-level and population-level transmission models. PrEP was found to be a cost-effective HIV-prevention intervention in high-risk MSM with HIV incidence at least 2% in the USA (<US$100 000 per quality-adjusted life year) and in young women in South Africa (cost per life year <GDP per capita). Results were sensitive to the cost and efficacy of PrEP and to assumptions about HIV testing and access to treatment in the absence of PrEP.

SUMMARY

Future cost effectiveness studies should consider PrEP implementation issues (uptake in high-risk versus low-risk groups, duration on PrEP, adherence), budget impact, and the role of PrEP as part of combination HIV-prevention strategies including expanded testing and treatment access.

Systematic review of HIV transmission between heterosexual serodiscordant couples where the HIV-positive partner is fully suppressed on antiretroviral therapy

BACKGROUND

The risk of sexual HIV transmission in serodiscordant couples when the HIV-positive partner has full virologic suppression on combination antiretroviral therapy (cART) is debated. This study aims to systematically review observational studies and randomized controlled trials (RCTs), evaluating rates of sexual HIV transmission between heterosexual serodiscordant couples when the HIV-positive partner has full suppression on cART.

METHODS AND FINDINGS

We searched major bibliographic databases to November 2012 for relevant observational studies and RCTs without language restrictions. Conference proceedings, key journals and bibliographies were also searched. Studies reporting HIV transmission rates, cART histories and viral loads of the HIV-positive partners were included. Two reviewers extracted methodologic characteristics and outcomes. Of 20,252 citations, 3 studies met all eligibility criteria with confirmed full virologic suppression in the HIV-positive partner. We included 3 additional studies (2 cohort studies, 1 RCT) that did not confirm viral suppression in the HIV-positive partner at transmission in a secondary meta-analysis. Methodologic quality was reasonable. The rate of transmission in the 3 studies confirming virologic suppression was 0 per 100 person-years (95% CI = 0-0.05), with low heterogeneity (I(2) = 0%). When we included the 3 studies that did not confirm virologic suppression, the rate of transmission was 0.14 per 100 person-years (95%CI = 0.04-0.31) (I(2) = 0%). In a sensitivity analysis including all 6 studies, the rate of transmission was 0 per 100 person-years (95%CI = 0-0.01) after omitting all transmissions with known detectable or unconfirmed viral loads, as full suppression in these cases was unlikely. Limitations included lack of data on same-sex couples, type of sexual intercourse (vaginal vs. anal), direction of HIV transmission, exact viral load at the time of transmission, sexually transmitted infections (STI) rates, and extent of condom use.

CONCLUSIONS

Our findings suggest minimal risk of sexual HIV transmission for heterosexual serodiscordant couples when the HIV-positive partner has full viral suppression on cART with caveats regarding information on sexual intercourse type, STIs, and condom use. These findings have implications when counseling heterosexual serodiscordant couples on sexual and reproductive health. More research is needed to explore HIV transmission risk between same-sex couples.

Reaping the prevention benefits of highly active antiretroviral treatment: policy implications of HIV Prevention Trials Network 052

PURPOSE OF REVIEW

This review explores the policy implications of findings from the HIV Prevention Trials Network (HPTN 052) treatment as prevention (TasP) study.

RECENT FINDINGS

To date, the potential of antiretrovirals to prevent sexual transmission of HIV by infected persons has been grounded in observational cohort, ecological, mathematical modeling, and meta-analytic studies. HPTN 052 represents the first randomized controlled trial to test the secondary prevention benefit of HIV transmission using antiretroviral treatment in largely asymptomatic persons with high CD4 cell counts.

SUMMARY

The US National HIV/AIDS Strategy has among its key goals the reduction of incident HIV infections, improved access to quality care and associated outcomes, and the reduction in HIV-associated health disparities and inequities. HPTN 052 demonstrates that providing TasP, in combination with other effective prevention strategies offers the promise of achieving these life-saving goals. But HPTN 052 also highlights the need for cautious optimism and underscores the importance of addressing current gaps in the HIV prevention, treatment, and care continuum in order for 'TasP' strategies to achieve their full potential. Among these are necessary improvements in the capacity to expand HIV testing, facilitate effective linkage and retention in care, and improve treatment initiation, maintenance, and virus suppression.

Beyond the distinction between biomedical and social dimensions of HIV prevention through the lens of a social public health

Developing effective HIV prevention requires that we move beyond the historical but problematic distinction between biomedical and social dimensions of HIV. The current claim that prevention has failed has led to a strong interest in the role of treatment as HIV prevention; however, the turn to "biomedical prevention," "test and treat," and "combination prevention" instances pervasive confusions about prevention. These confusions arise from a failure to realize that all HIV prevention interventions must engage with the everyday lives of people and be integrated into their social relations and social practices. We challenge the claim that prevention has failed (illustrating this with discussion of prevention in Australia, Uganda, and Zimbabwe). We explain the enduring appeal of misguided approaches to prevention by examining how 1996 can be seen as a pivotal moment in the history of the global response to HIV, a moment marked by the rise and fall of distinct biomedical and social narratives of HIV.

Male circumcision for HIV prevention: current evidence and implementation in sub-Saharan Africa

Heterosexual exposure accounts for most HIV transmission in sub-Saharan Africa, and this mode, as a proportion of new infections, is escalating globally. The scientific evidence accumulated over more than 20 years shows that among the strategies advocated during this period for HIV prevention, male circumcision is one of, if not, the most efficacious epidemiologically, as well as cost-wise. Despite this, and recommendation of the procedure by global policy makers, national implementation has been slow. Additionally, some are not convinced of the protective effect of male circumcision and there are also reports, unsupported by evidence, that non-sex-related drivers play a major role in HIV transmission in sub-Saharan Africa. Here, we provide a critical evaluation of the state of the current evidence for male circumcision in reducing HIV infection in light of established transmission drivers, provide an update on programmes now in place in this region, and explain why policies based on established scientific evidence should be prioritized. We conclude that the evidence supports the need to accelerate the implementation of medical male circumcision programmes for HIV prevention in generalized heterosexual epidemics, as well as in countering the growing heterosexual transmission in countries where HIV prevalence is presently low.

Two sides to the HIV prevention coin: efficacy and effectiveness

In the context of the current concern about HIV prevention efforts, this article addresses the issues of efficacy and effectiveness. We argue that the success of treatments and associated increasing dominance of biomedicine has meant that far too little attention has been paid to effectiveness, that is, to the impact an HIV prevention program or intervention achieves in the real world, under resource constraints, in entire populations. Although biomedicine has, appropriately, investigated the efficacy of a number of new prevention technologies and modeled the impact of "test and treat," issues relating to the provision, acceptability, adoption, and sustained use of prevention technologies, both old and new, have not been fully addressed. As HIV is a profoundly social disease with its causes and consequences deeply embedded in social, cultural and political processes, social scientists need to be heard and work with biomedical scientists to ensure the success of HIV prevention.

Universal testing and treatment as an HIV prevention strategy: research questions and methods

Achieving high coverage of antiretroviral treatment (ART) in resource-poor settings will become increasingly difficult unless HIV incidence can be reduced substantially. Universal voluntary counselling and testing followed by immediate initiation of ART for all those diagnosed HIV-positive (universal testing and treatment, UTT) has the potential to reduce HIV incidence dramatically but would be very challenging and costly to deliver in the short term. Early modelling work in this field has been criticised for making unduly optimistic assumptions about the uptake and coverage of interventions. In future work, it is important that model parameters are realistic and based where possible on empirical data. Rigorous research evidence is needed before the UTT approach could be considered for wide-scale implementation. This paper reviews the main areas that need to be explored. We consider in turn research questions related to the provision of services for universal testing, services for immediate treatment of HIV-positives and the population-level impact of UTT, and the research methods that could be used to address these questions. Ideally, initial feasibility studies should be carried out to investigate the acceptability, feasibility and uptake of UTT services. If these studies produce promising results, there would be a strong case for a cluster-randomised trial to measure the impact of a UTT intervention on HIV incidence, and we consider the main design features of such a trial.

Antiretroviral therapy: a key component of a comprehensive HIV prevention strategy

Transmission of HIV is critically dependent on the level of HIV viral load within blood and genital secretions. Antiretroviral therapy results in sustained reductions in viral load to undetectable levels. Thus, antiretroviral therapy has long been postulated as a potential means to curb HIV transmission. Observational data have now confirmed that antiretroviral therapy is associated with a decrease in transmission among heterosexual serodiscordant couples, injection-drug users, and in population-based studies. Mathematical models suggest that further expansion of antiretroviral coverage within current guidelines can play a major role in controlling the spread of HIV. Concerns regarding the potential for transmission during acute HIV infection, behavioral disinhibition, and resistance to overcome the impact of treatment on prevention have not materialized to date. The Joint United Nations AIDS (UNAIDS) program has called for the inclusion of antiretroviral treatment as a key pillar in the global strategy to control the spread of HIV infection.

Interaction of mathematical modeling and social and behavioral HIV/AIDS research

PURPOSE OF REVIEW

HIV is transmitted within complex biobehavioral systems. Mathematical modeling can provide insight to complex population-level outcomes of various behaviors measured at an individual level.

RECENT FINDINGS

HIV models in the social and behavioral sciences can be categorized in a number of ways; here, we consider two classes of applications common in the field generally, and in the past year in particular: those models that explore significant behavioral determinants of HIV disparities within and between populations; and those models that seek to evaluate the potential impact of specific social and behavioral interventions.

SUMMARY

We discuss two overarching issues we see in the field: the need to further systematize effectiveness models of behavioral interventions, and the need for increasing investigation of the use of behavioral data in epidemic models. We believe that a recent initiative by the National Institutes of Health will qualitatively change the relationships between epidemic modeling and sociobehavioral prevention research in the coming years.