Model-based evaluation of HIV prevention interventions

Microfinance for women at high risk for HIV in Kazakhstan: study protocol for a cluster-randomized controlled trial

BACKGROUND

Among women at high risk for HIV and other sexually transmitted diseases (STIs), gender and economic issues limit the impact of behavioral prevention strategies. Women in Kazakhstan with dual risks of sex trading and drug use face elevated risk for HIV and STIs and may benefit from an economic empowerment intervention which combines HIV-risk reduction (HIVRR) education with financial skills-building and asset-building to promote reduced reliance on sex trading for income.

METHODS/DESIGN

The study employs a two-arm, cluster-randomized controlled trial (c-RCT) design. We will use cluster randomization to assign 350 women in approximately 50 cohorts to a traditional four-session HIV-risk-reduction intervention combined with a six-session financial literacy intervention, enrollment in a 24-session vocational training program and receipt of matched savings (HIVRR+MF); or to the four-session HIV-risk-reduction intervention alone (HIVRR). Repeated behavioral and biological assessments will be conducted at baseline, then at 6, 9, and 15 months post randomization/session 1.

DISCUSSION

This study responds to an identified need in the academic literature for rigorous testing of structural interventions, including combination microfinance and HIV-prevention interventions.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT02406482 . Registered on 30 March 2015.

Differentiated Human Immunodeficiency Virus RNA Monitoring in Resource-Limited Settings: An Economic Analysis

Background.

Viral load (VL) monitoring for patients receiving antiretroviral therapy (ART) is recommended worldwide. However, the costs of frequent monitoring are a barrier to implementation in resource-limited settings. The extent to which personalized monitoring frequencies may be cost-effective is unknown.

Methods.

We created a simulation model parameterized using person-level longitudinal data to assess the benefits of flexible monitoring frequencies. Our data-driven model tracked human immunodeficiency virus (HIV)–infected individuals for 10 years following ART initiation. We optimized the interval between viral load tests as a function of patients’ age, gender, education, duration since ART initiation, adherence behavior, and the cost-effectiveness threshold. We compared the cost-effectiveness of the personalized monitoring strategies to fixed monitoring intervals every 1, 3, 6, 12, and 24 months.

Results.

Shorter fixed VL monitoring intervals yielded increasing benefits (6.034 to 6.221 discounted quality-adjusted life-years [QALYs] per patient with monitoring every 24 to 1 month over 10 years, respectively, standard error = 0.005 QALY), at increasing average costs: US$3445 (annual monitoring) to US$5393 (monthly monitoring) per patient, respectively (standard error = US$3.7). The adaptive policy optimized for low-income contexts achieved 6.142 average QALYs at a cost of US$3524, similar to the fixed 12-month policy (6.135 QALYs, US$3518). The adaptive policy optimized for middle-income resource settings yields 0.008 fewer QALYs per person, but saves US$204 compared to monitoring every 3 months.

Conclusions.

The benefits from implementing adaptive vs fixed VL monitoring policies increase with the availability of resources. In low- and middle-income countries, adaptive policies achieve similar outcomes to simpler, fixed-interval policies.

Cost Effectiveness of HIV Prevention Interventions in the U.S

INTRODUCTION

The purpose of this study was to assess and compare the cost effectiveness of current HIV prevention interventions in the U.S. using a consistent, standardized methodology.

METHODS

The cost effectiveness of common and emerging HIV biomedical and behavioral prevention interventions as delivered to men who have sex with men, injection drug users, and sexually active heterosexuals was estimated. Data on program costs, intervention efficacy, risk behaviors, and per contact transmission probabilities were collected from peer-reviewed papers and health department reports. These data were combined with 2010 national HIV incidence and prevalence surveillance data in a Bernoulli process model to estimate the reduced annual risk of HIV transmission or acquisition associated with these interventions. The cost per prevented case of HIV and the cost per saved quality-adjusted life year were then calculated. Analyses were conducted between 2014 and 2015.

RESULTS

Interventions to diagnose HIV and provide ongoing care and treatment had the lowest cost per prevented case. Among interventions targeted at specific risk groups, interventions for men who have sex with men were the most cost effective. The least cost-effective interventions typically addressed people at risk of acquiring HIV rather than those at risk of transmitting the disease.

CONCLUSIONS

HIV prevention interventions targeted at high-risk populations, those associated with the care continuum, and those that reduce the transmission risk of HIV-infected people are typically the most cost effective. Decision makers can consider these results in planning an efficient allocation of HIV prevention resources.

Cost-effectiveness of interventions to prevent HIV and STDs among women: a randomized controlled trial

Injection drug use is a leading transmission route of HIV and STDs, and disease prevention among drug users is an important public health concern. This study assesses cost-effectiveness of behavioral interventions for reducing HIV and STDs infections among injection drug-using women. Cost-effectiveness analysis was conducted from societal and provider perspectives for randomized trial data and Bernoullian model estimates of infections averted for three increasingly intensive interventions: (1) NIDA's standard intervention (SI); (2) SI plus a well woman exam (WWE); and (3) SI, WWE, plus four educational sessions (4ES). Trial results indicate that 4ES was cost-effective relative to WWE, which was dominated by SI, for most diseases. Model estimates, however, suggest that WWE was cost-effective relative to SI and dominated 4ES for all diseases. Trial and model results agree that WWE is cost-effective relative to SI per hepatitis C infection averted ($109 308 for in trial, $6 016 in model) and per gonorrhea infection averted ($9 461 in trial, $14 044 in model). In sensitivity analysis, trial results are sensitive to 5 % change in WWE effectiveness relative to SI for hepatitis C and HIV. In the model, WWE remained cost-effective or cost-saving relative to SI for HIV prevention across a range of assumptions. WWE is cost-effective relative to SI for preventing hepatitis C and gonorrhea. WWE may have similar effects as the costlier 4ES.

Effectiveness of Couple-Based HIV Counseling and Testing for Women Substance Users and Their Primary Male Partners: A Randomized Trial

A randomized trial was conducted to test the effectiveness of couple-based HIV counseling and testing (CB-HIV-CT) and women-only relationship-focused HIV counseling and testing (WRF-HIV-CT) in reducing HIV risk compared to the National Institute on Drug Abuse HIV-CT standard intervention. Substance using HIV-negative women and their primary heterosexual partner (N = 330 couples) were randomized to 1 of the 3 interventions. Follow-up assessments measuring HIV risk behaviors and other relevant variables were conducted at 3- and 9-months postintervention. Repeated measures generalized linear mixed model analysis was used to assess treatment effects. A significant reduction in HIV risk was observed over the 9-month assessment in the CB-HIV-CT group compared to that of the control group (b = -0.51, t[527] = -3.20, P = 0.002) and compared to that of the WRF-HIV-CT group (b = -0.34, t[527] = -2.07, P = 0.04), but no significant difference was observed between WRF-HIV-CT and controls (b = -0.17, t[527] = -1.09, P = 0.28). A brief couple-based HIV counseling and testing intervention designed to address both drug-related and sexual risk behaviors among substance using women and their primary male partners was shown to be more effective at reducing overall HIV risk compared to a standard HIV-CT intervention in an urban setting.

Quantifying sexual exposure to HIV within an HIV-serodiscordant relationship: development of an algorithm

BACKGROUND

The risk of acquiring HIV from a single sexual contact varies enormously reflecting biological and behavioural characteristics of both infected and uninfected partners. Accurate information on HIV transmission risk is required to construct evidence-based risk reduction practices for individuals, to direct the provision of prevention strategies at the population level, and enable the definition, quantification and comparison of true exposure in individuals termed 'exposed uninfected' within clinical trials.

METHODS

Following a systematic review of current literature on HIV transmission estimates, an HIV risk score was developed, incorporating weighted risk factors into a Bernoulli mathematical model, allowing quantification of overall risk of HIV acquisition within HIV-serodiscordant partnerships.

RESULTS

The HIV risk score enumerates the relative risk of HIV acquisition from HIV-positive partners incorporating the type and frequency of specific sex acts, the index case HIV plasma viral load and stage of disease, and the presence of genital ulcer disease in either partner and pregnancy, HSV-2 seropositivity, and circumcision status (men only) in the HIV-negative partner.

CONCLUSION

Key determinants of HIV exposure risk can be incorporated into a mathematical model in order to quantify individual relative risks of HIV acquisition. Such a model can facilitate comparisons within clinical trials of exposed uninfected individuals and facilitate interventions to reduce HIV transmission.

Aggregate versus individual-level sexual behavior assessment: how much detail is needed to accurately estimate HIV/STI risk?

The sexual behaviors of HIV/sexually transmitted infection (STI) prevention intervention participants can be assessed on a partner-by-partner basis: in aggregate (i.e., total numbers of sex acts, collapsed across partners) or using a combination of these two methods (e.g., assessing five partners in detail and any remaining partners in aggregate). There is a natural trade-off between the level of sexual behavior detail and the precision of HIV/STI acquisition risk estimates. The results of this study indicate that relatively simple aggregate data collection techniques suffice to adequately estimate HIV risk. For highly infectious STIs, in contrast, accurate STI risk assessment requires more intensive partner-by-partner methods.

Sexual transmission of HIV-1

HIV-1 transmission occurs in a limited number of ways all of which are preventable. Overall, the risk of HIV-1 transmission following a single sexual exposure is low especially in comparison with other sexually transmitted infections (STIs); with estimates of the average probability of male to female HIV-1 transmission only 0.0005-0.0026 per coital act. The risk of acquiring HIV-1 from a single contact varies enormously and is dependant upon the infectiousness of the HIV-1 positive individual and the susceptibility to HIV-1 of their sexual partner. An understanding of the determinants of HIV-1 transmission is important not only to assess the infection risk to an individual when exposed to the virus (e.g. to determine the provision of post exposure prophylaxis), but also to make accurate predictions on the potential spread of HIV-1 infection in a population and to direct appropriate targeted prevention strategies. In this review article we summarise the current literature on the major worldwide source of HIV-1 acquisition, sexual transmission. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

Probability of HIV transmission during acute infection in Rakai, Uganda

Accurate estimates of the probability of HIV transmission during various stages of infection are needed to inform epidemiological models. Very limited information is available about the probability of transmission during acute HIV infection. We conducted a secondary analysis of published data from the Rakai, Uganda seroconversion study. Mathematical and computer-based models were used to quantify the per-act and per-partnership transmission probabilities during acute and chronic HIV infection, and to estimate how many of the transmission events reported in the Rakai study were due to acute-phase HIV transmission. The average per-act transmission probability during acute infection equaled 0.03604 vs. 0.00084 for chronic HIV infection. Overall, HIV was transmitted during acute infection in 46.5% of 23 "incident index partner couples." Acute-phase transmission accounted for 89.1% of all transmission events in the first 20 months of follow-up. These results highlight the substantial risk of transmission during acute HIV infection.

Programmes, resources, and needs of HIV-prevention nongovernmental organizations (NGOs) in Africa, Central/Eastern Europe and Central Asia, Latin America and the Caribbean

This study assessed the programmes, resources, and needs of HIV-prevention nongovernmental organizations (NGOs) in 75 countries in Africa, Central/Eastern Europe and Central Asia, Latin America and the Caribbean. Multiple databases and expert recommendations were used to identify one major HIV-prevention NGO in the capital or a large city in each country, and in-depth interviews were conducted with each NGO Director. Most NGOs are carrying out their programmes with minimal funding and few regularly employed personnel. Most are highly dependent on international donors, but reliance on small grants with short funding periods limits programme development capacity. HIV-prevention activities varied by region, with African NGOs most likely to use peer education and community awareness events; Eastern European NGOs most likely to offer needle exchange; Latin American NGOs to have resource centres and offer risk reduction programmes; and Caribbean organizations to use mass education approaches. Across regions, NGOs most often targeted the general public and youth, although specialized at-risk groups were the additional focus of attention in some regions. Limited funding, governmental indifference or opposition, AIDS stigma, and social discomfort discussing sex were often cited as barriers to new HIV-prevention programmes. NGOs are critical service providers. However, their funding, programmes, and resource capacities must be strengthened if NGOs are to realize their full potential in HIV prevention.

Economic Evaluation of an HIV Prevention Intervention for Seropositive Injection Drug Users

OBJECTIVE

To assess the cost-effectiveness of Intervention for HIV-Seropositive injection drug users--Research and Evaluation (INSPIRE), designed to reduce risky sexual and needle-sharing behaviors in research sites in four US cities (2001-2003).

METHODS

We collected data on program and participant costs. We used a mathematical model to estimate the number of sex partners of injection drug users expected to become infected with human immunodeficiency virus (HIV) (with and without intervention), cost of treatment for sex partners who became infected, and the effect of infection on partners' quality-adjusted life expectancy. We determined the minimum effect that INSPIRE must have on condom use among participants for the intervention to be cost-saving (intervention cost less than savings from averted HIV infections) or cost-effective (net cost per quality-adjusted life year saved less than $50,000).

RESULTS

The intervention cost was $870 per participant. It would be cost-saving if it led to 53 percent reduction in the proportion of participants who had any unprotected sex in 1 year and cost-effective with 17 percent reduction. If behavior change lasted 3 months, the cost-effectiveness threshold was 66 percent; if 3 years, the threshold was 6 percent.

CONCLUSIONS

Although cost-saving thresholds may not be achievable by the intervention, we anticipate that cost-effectiveness thresholds will be attained.

An empirical study of ordinal condom use measures

Accurate condom use assessment is critical in sexually transmitted infection-prevention research. Ordinal condom use frequency measures may be problematic due to subjective interpretation by respondents. To assess this potential bias, we examined the ordinal condom use labels (e.g., "never," "rarely," etc.) assigned by college students to 17 scenarios that described how frequently a hypothetical couple used condoms. Scenarios varied by condom use frequency (0% to 100%) and by whether frequency was described by stating the number of protected acts out of 20 total acts of intercourse, out of 100 total acts, or as a proportion of acts that were protected. There was substantial interpersonal variability in the labels assigned by participants in all 17 scenarios and inconsistent use of the "never" and "always" labels to characterize 0% and 100% condom use, respectively. The assigned labels varied as a function of the number of total acts (20 vs. 100) and whether condom use was expressed as a count or a percentage, which suggests that participants did not convert the number of protected acts to an equivalent proportion. These results call into question both the reliability and validity of ordinal condom use measures.

Cost-Effectiveness of a Community-Level HIV Risk Reduction Intervention for Women Living in Low-Income Housing Developments

We conducted a cost-effectiveness analysis of a multi-site community-level HIV prevention trial that enrolled women living in 18 low-income housing developments in 5 U.S. cities. A mathematical model of HIV transmission was used to estimate the number of HIV infections averted and quality-adjusted life years (QALYs) saved by the community-level intervention, based on data obtained from community-wide sexual behavior surveys at baseline and 12-month follow-up. Results indicated that the intervention prevented approximately 1 infection per 3500 women reached by the intervention, at a total cost of 174,845 dollars. The cost per QALY saved by the intervention was 37,433 dollars and the cost per HIV infection averted was 732,072 dollars. The community-level intervention was moderately cost-effective in comparison with other HIV prevention programs for at-risk women. Synergistic approaches to HIV prevention that combine community-level sexual norm change interventions with more intensive risk reduction programs for high-risk women are needed. EDITORS' STRATEGIC IMPLICATIONS: The authors present a promising and efficient community-level HIV prevention approach, with effects beyond the limited scope of individual or small group interventions. This paper represents an example of how an analysis of cost-effectiveness can provide policymakers with information needed for difficult decisions about prevention resource allocations.

A rapid assessment of community-wide HIV/STI intervention in China

BACKGROUND/OBJECTIVES

The key to HIV/STI control is community-wide intervention (CWI) which depends heavily on continuous monitoring and evaluation. Unfortunately, comprehensive CWI assessment methodology and reports are generally lacking. This study developed, applied, and evaluated a rapid tool for assessing CWI in China.

METHODS

A total of 120 county level respondents in charge of county-wide responses to HIV/STI throughout China were selected randomly and surveyed using a structured inventory consisting of three tiers of indicators developed via consensus group techniques. The respondents were asked to rate each of the indicators against a five grade (1-5) scale. 30 pairs of the same staff from within Anhui Province were surveyed to gauge inter-rater reliability.

RESULTS

Response rate for the nationwide survey was 85% and for inter-rater reliability survey, 90%. Correlation coefficients between the inter-rater ratings ranged from 0.68 to 0.95. The overall average rating of CWI in China was 2.85. Average ratings for the six first tier indicators, organisation and policy development, goals and objectives setting, project and action planning, resource exploitation, project and task implementation, and CWI evaluation were 2.87, 2.83, 2.67, 2.77, 3.26, and 2.71 respectively. Ratings derived for the 24 second tier indicators ranged from 2.1 to 3.86; while for the 96 third tier indicators, 1.90 to 4.40

CONCLUSIONS

The instrument developed proved to be reliable, useful, and easily applicable in common communities. Application of it in China revealed that a large gap exists between desired and actual CWI, and areas meriting particular attention include policy and incentives development, intervention planning and evaluation, and fund raising and utilisation.

Health and Economic Impacts of an HIV Intervention in Out of Treatment Substance Abusers: Evidence from a Dynamic Model

INTRODUCTION

A community-based intervention program found that the high-risk target population interacts with its surrounding community as a source of drugs and prostitution, creating a measure of co-dependence in the health status of each group.

METHODOLOGY

The intervention collected extensive data on sexual and drug use practices in the target population. A dynamic compartment model estimates the epidemiological impact of the intervention, which serves as the basis for the economic assessment comparing intervention costs and lifetime HIV treatment costs.

RESULTS

Approximately 2/3 of the new infections arise in the surrounding community. Intervention spillover benefits in the surrounding community are sufficient to make the intervention cost-saving in the first year--a savings of approximately 534,000 dollars.

CONCLUSIONS

Conducting the intervention results in health benefits and cost-savings not only for the risk group, but for the entire community in which it resides. Quantifying the spillovers is vital to policymakers attempting to allocate scarce public health resources.

Comparing the Cost-Effectiveness of HIV Prevention Interventions

OBJECTIVE

Communities need to identify cost-effective interventions for HIV prevention to optimize limited resources.

METHODS

The authors developed a spreadsheet tool using Bernoulli and proportionate change models to estimate the relative cost-effectiveness for 26 HIV prevention interventions including biomedical interventions, structural interventions, and interventions designed to change risk behaviors of individuals. They also conducted sensitivity analyses to assess patterns of the cost-effectiveness across different populations using various assumptions.

RESULTS

The 2 factors most strongly determining the cost-effectiveness of the different interventions were the HIV prevalence of the population at risk and the cost per person reached. In low-prevalence populations (eg, heterosexuals) the most cost-effective interventions were structural interventions (eg, mass media, condom distribution), whereas in high-prevalence populations (eg, men who have sex with men) individually focused interventions to change risk behavior were also relatively cost-effective. Among the most cost-effective interventions overall were showing videos in STD clinics and raising alcohol taxes. School-based HIV prevention programs appeared to be the least cost-effective. Needle exchange and needle deregulation programs were relatively cost-effective only when injection drug users have a high HIV prevalence.

CONCLUSIONS

Comparing estimates of the cost-effectiveness of HIV interventions provides insight that can help local communities maximize the impact of their HIV prevention resources.

Utility of behavioral changes as markers of sexually transmitted disease risk reduction in sexually transmitted disease/HIV prevention trials

Most sexually transmitted disease (STD)/HIV sexual risk reduction intervention trials are evaluated using behavioral outcomes as their main indicators of intervention effectiveness. How good are behavioral measures as surrogate markers for STD infection? Do the behavioral changes that are commonly assessed in risk reduction interventions accurately reflect changes in STD risk? We applied a mathematical model of STD/HIV transmission to empiric data from a large HIV prevention intervention to estimate pre- to postintervention changes in intervention participants' STD risk. We then used the coefficient of determination (R(2)) to assess the strength of association between changes in STD risk and changes in three behavioral measures: proportion of acts of intercourse for which condoms were used, number of sex partners, and number of acts of unprotected intercourse. The results indicate that change in the number of acts of unprotected intercourse is a superior marker of STD risk changes for less infectious STDs such as HIV, whereas change in the number of partners may be preferable for highly infectious STDs such as gonorrhea. Changes in the proportion of acts of intercourse for which condoms were used were not strongly correlated with changes in STD risk under most of the conditions examined in this analysis. The utility of different measures of sexual behavior change as markers for changes in STD risk and, hence, expected incidence, depends on the infectivity and prevalence of the target STD.

Using sexually transmitted disease incidence as a surrogate marker for HIV incidence in prevention trials: a modeling study

BACKGROUND

Because many of the sexual behaviors that place individuals at risk of acquiring HIV are the same as those that place them at risk for other sexually transmitted diseases (STDs), researchers and policymakers have called for the use of non-HIV STDs as surrogate markers for HIV infection.

GOALS

This study examined the epidemiologic conditions under which changes in STD incidence are associated with changes in HIV incidence.

STUDY DESIGN

A mathematical model of HIV/STD transmission was applied to empirical data from a large HIV prevention intervention. The association between participants' HIV infection risk reduction scores and their STD risk reduction scores was measured with use of the Pearson product-moment correlation. The authors examined how the strength of association varied across different epidemiologic parameters and heterosexual behaviors.

RESULTS

Moderate to strong associations were noted when the infectivity of the STD was similar to the infectivity of HIV. The association was attenuated for larger STD infectivity values. The prevalence of STD infection was a less important determinant of the strength of association. Stronger associations were obtained when the number of sex partners was large or the number of sex acts was small.

CONCLUSIONS

Easily transmitted STDs, such as gonorrhea, are unsuitable for general use as surrogate markers for HIV infection. Hepatitis B, syphilis, and chlamydial infection have more promising epidemiologic profiles. Careful studies of STD infectivity are needed to aid in the identification of potential marker STDs.

Probabilistic cost-effectiveness analysis of HIV prevention. Comparing a Bayesian approach with traditional deterministic sensitivity analysis

In cost-effectiveness analysis, the incremental cost-effectiveness ratio is used to measure economic efficiency of a new intervention, relative to an existing one. However, costs and effects are seldom known with certainty. Uncertainty arises from two main sources: uncertainty regarding correct values of intervention-related parameters and uncertainty associated with sampling variation. Recently, attention has focused on Bayesian techniques for quantifying uncertainty. We computed the Bayesian-based 95% credible interval estimates of the incremental cost-effectiveness ratio of several related HIV prevention interventions and compared these results with univariate sensitivity analyses. The conclusions were comparable, even though the probabilistic technique provided additional information.

Using cost-effectiveness league tables to compare interventions to prevent sexual transmission of HIV

Cost-effectiveness information is needed to help public health decision makers choose between competing HIV prevention programs. One way to organize this information is in a 'league table' that lists cost-effectiveness ratios for different interventions and which facilitates comparisons across interventions. Herein we propose a common outcome measure for use in HIV prevention league tables and present a preliminary league table of interventions to reduce sexual transmission of HIV in the US. Fifteen studies encompassing 29 intervention for different population groups are included in the table. Approximately half of the interventions are cost-saving (i.e. save society money, in the long run), and three-quarters are cost-effective by conventional standards. We discuss the utility of such a table for informing the HIV prevention resource allocation process and delineate some of the difficulties associated with the league table approach, especially as applied to HIV prevention cost-effectiveness analysis.

A relative risk-based, disease-specific definition of sexual abstinence failure rates

Sexual abstinence programs have the potential to reduce the incidence of unplanned pregnancies and sexually transmitted diseases (STDs) among adolescents. Effectiveness measures are needed to help researchers assess the impact of sexual abstinence promotion programs on STD and pregnancy rates and to enable comparisons of abstinence effectiveness with other contraception and STD prevention methods. Abstinence "failure rates" have been proposed as one measure of program effectiveness. However, the concept of abstinence failure rates has not been adequately operationalized. The present study examines a novel mathematical framework for estimating abstinence failure rates, both theoretically and empirically. Examples are provided, and the advantages and disadvantages associated with the mathematical model-based approach are discussed.

Economic evaluation of HIV risk reduction intervention in African-American male adolescents

PURPOSE

To evaluate the cost-effectiveness of a cognitive-behavioral HIV risk reduction intervention for African-American male adolescents that has previously been shown to be effective at reducing sexual risk taking.

METHODS

Standard techniques of cost-utility analysis were employed. A societal perspective and a 3% discount rate were used in the main analysis. Program costs were ascertained retrospectively. A mathematical model of HIV transmission was used to translate observed changes in sexual behavior into an estimate of the number of HIV infections the intervention averted. Intervention effects were assumed to last for 1 year. For each infection averted, the corresponding savings in future HIV-related medical care costs and quality-adjusted life years (QALYs) were estimated. The overall net cost per QALY saved (cost-utility ratio) was then calculated. Sensitivity analyses were performed to assess the robustness of the main results.

RESULTS

The cost-utility ratio was approximately $57,000 U.S. per QALY saved when training costs were included, and $41,000 U.S. per QALY saved when they were excluded. The intervention appeared substantially more cost-effective when the analysis was restricted to the subgroup of participants who reported being sexually active at baseline. Assumptions about the prevalence of HIV infection and the duration of intervention effectiveness also greatly affected the cost-utility ratio.

CONCLUSIONS

The HIV prevention intervention was moderately cost-effective in comparison with other health care programs. Selectively implementing the intervention in high-HIV prevalence communities and with sexually active youth can enhance cost-effectiveness.

Cost-threshold analyses of the National AIDS Demonstration Research HIV prevention interventions

OBJECTIVE

The goal of the multisite National AIDS Demonstration Research (NADR) program was to reduce the sexual and drug injection-related HIV risks of out-of-treatment injection drug users and their sex partners. Previous analyses have established that the NADR interventions were effective at changing participants' risky behaviors. This study was to determine whether the NADR program also was cost-effective.

METHODS

Data from eight NADR study sites were included in the analysis. A mathematical model was used to translate reported sexual and injection-related behavior changes into an estimate of the number of infections prevented by the NADR interventions and then to calculate the corresponding savings in averted HIV/AIDS medical care costs and quality-adjusted years of life, assuming United States values for these parameters. Because cost data were not collected in the original NADR evaluation, the savings in averted medical care costs were compared with the cost of implementing a similar intervention program for injection drug users.

RESULTS

The eight NADR interventions prevented approximately 129 infections among 6629 participants and their partners. Overall, the NADR program would be cost saving (i.e. provide net economic savings) if it cost less than US$2107 per person and would be cost-effective if it cost less than US$10,264 per person. Both of these estimates are considerably larger than the US$273 per person cost of the comparison intervention. There was substantial cross-site variability.

CONCLUSIONS

The results of this analysis strongly suggest that the NADR interventions were cost-saving overall and were, at the very least, cost-effective at all eight sites. In the United States and other developed counties, investments in HIV-prevention interventions such as these have the potential to save substantial economic resources by averting HIV-related medical care expenses among injection drug users.

When is an HIV infection prevented and when is it merely delayed?

HIV prevention programs are typically evaluated using behavioral outcomes. Mathematical models of HIV transmission can be used to translate these behavioral outcomes into estimates of the number of HIV infections averted. Usually, intervention effectiveness is evaluated over a brief assessment period and an infection is considered to be prevented if it does not occur during this period. This approach may overestimate intervention effectiveness if participants continue to engage in risk behaviors. Conversely, this strategy underestimates the true impact of interventions by assuming that behavioral changes persist only until the end of the intervention assessment period. In this article, the authors (a) suggest a simple framework for distinguishing between HIV infections that are truly prevented and those that are merely delayed, (b) illustrate how these outcomes can be estimated, (c) discuss strategies for extrapolating intervention effects beyond the assessment period, and (d) highlight the implications of these findings for HIV prevention decision making.