[show abstract][hide abstract] ABSTRACT: There is urgent need for effective HIV prevention methods that women can initiate. The CAPRISA 004 trial showed that a tenofovir-based vaginal microbicide had significant impact on HIV incidence among women. This study uses the trial findings to estimate the population-level impact of the gel on HIV and HSV-2 transmission, and price thresholds at which widespread product introduction would be as cost-effective as male circumcision in urban South Africa.
The estimated 'per sex-act' HIV and HSV-2 efficacies were imputed from CAPRISA 004. A dynamic HIV/STI transmission model, parameterised and fitted to Gauteng (HIV prevalence of 16.9% in 2008), South Africa, was used to estimate the impact of gel use over 15 years. Uptake was assumed to increase linearly to 30% over 10 years, with gel use in 72% of sex-acts. Full economic programme and averted HIV treatment costs were modelled. Cost per DALY averted is estimated and a microbicide price that equalises its cost-effectiveness to that of male circumcision is estimated.
Using plausible assumptions about product introduction, we predict that tenofovir gel use could lead to a 12.5% and 4.9% reduction in HIV and HSV-2 incidence respectively, by year 15. Microbicide introduction is predicted to be highly cost-effective (under $300 per DALY averted), though the dose price would need to be just $0.12 to be equally cost-effective as male circumcision. A single dose or highly effective (83% HIV efficacy per sex-act) regimen would allow for more realistic threshold prices ($0.25 and $0.33 per dose, respectively).
These findings show that an effective coitally-dependent microbicide could reduce HIV incidence by 12.5% in this setting, if current condom use is maintained. For microbicides to be in the range of the most cost-effective HIV prevention interventions, product costs will need to decrease substantially.
[show abstract][hide abstract] ABSTRACT: Background
New WHO guidelines recommend initiation of antiretroviral therapy for HIV-positive adults with CD4 counts of 500 cells per μL or less, a higher threshold than was previously recommended. Country decision makers have to decide whether to further expand eligibility for antiretroviral therapy accordingly. We aimed to assess the potential health benefits, costs, and cost-effectiveness of various eligibility criteria for adult antiretroviral therapy and expanded treatment coverage.
We used several independent mathematical models in four settings—South Africa (generalised epidemic, moderate antiretroviral therapy coverage), Zambia (generalised epidemic, high antiretroviral therapy coverage), India (concentrated epidemic, moderate antiretroviral therapy coverage), and Vietnam (concentrated epidemic, low antiretroviral therapy coverage)—to assess the potential health benefits, costs, and cost-effectiveness of various eligibility criteria for adult antiretroviral therapy under scenarios of existing and expanded treatment coverage, with results projected over 20 years. Analyses assessed the extension of eligibility to include individuals with CD4 counts of 500 cells per μL or less, or all HIV-positive adults, compared with the previous (2010) recommendation of initiation with CD4 counts of 350 cells per μL or less. We assessed costs from a health-system perspective, and calculated the incremental cost (in US$) per disability-adjusted life-year (DALY) averted to compare competing strategies. Strategies were regarded very cost effective if the cost per DALY averted was less than the country's 2012 per-head gross domestic product (GDP; South Africa: $8040; Zambia: $1425; India: $1489; Vietnam: $1407) and cost effective if the cost per DALY averted was less than three times the per-head GDP.
In South Africa, the cost per DALY averted of extending eligibility for antiretroviral therapy to adult patients with CD4 counts of 500 cells per μL or less ranged from $237 to $1691 per DALY averted compared with 2010 guidelines. In Zambia, expansion of eligibility to adults with a CD4 count threshold of 500 cells per μL ranged from improving health outcomes while reducing costs (ie, dominating the previous guidelines) to $749 per DALY averted. In both countries results were similar for expansion of eligibility to all HIV-positive adults, and when substantially expanded treatment coverage was assumed. Expansion of treatment coverage in the general population was also cost effective. In India, the cost for extending eligibility to all HIV-positive adults ranged from $131 to $241 per DALY averted, and in Vietnam extending eligibility to patients with CD4 counts of 500 cells per μL or less cost $290 per DALY averted. In concentrated epidemics, expanded access for key populations was also cost effective.
Our estimates suggest that earlier eligibility for antiretroviral therapy is very cost effective in low-income and middle-income settings, although these estimates should be revisited when more data become available. Scaling up antiretroviral therapy through earlier eligibility and expanded coverage should be considered alongside other high-priority health interventions competing for health budgets.
[show abstract][hide abstract] ABSTRACT: There has been discussion about whether individuals coinfected with HIV and hepatitis C virus (HCV) or hepatitis B virus (HBV) (∼30% of all people living with HIV) should be prioritized for early HIV antiretroviral therapy (ART). We assess the relative benefits of providing ART at CD4 count below 500 cells/μl or immediate ART to HCV/HIV or HBV/HIV-coinfected adults compared with HIV-monoinfected adults. We evaluate individual outcomes (HIV/liver disease progression) and preventive benefits in a generalized HIV epidemic setting.
We modeled disease progression for HIV-monoinfected, HBV/HIV-coinfected, and HCV/HIV-coinfected adults for differing ART eligibility thresholds (CD4 <350 cells/μl, CD4 <500 cells/μl, immediate ART eligibility upon infection). We report disability-adjusted life-years averted per 100 person-years on ART (DALYaverted/100PYonART) as a measure of the health benefits generated from incremental changes in ART eligibility. Sensitivity analyses explored impact on sexual HIV and vertical HIV, HCV, and HBV transmission.
For HBV/HIV-coinfected adults, a switch to ART initiation at CD4 count below 500 cells/μl from CD4 below 350 cells/μl generates 9% greater health benefits per year on ART (48 DALYaverted/100PYonART) than for HIV-monoinfected adults (44 DALYaverted/100PYonART). Additionally, ART at CD4 below 500 cells/μl could prevent 25% and 32% of vertical transmissions of HIV and HBV, respectively. For HCV/HIV-coinfected adults, ART at CD4 below 500 cells/μl generates 10% fewer health benefits (40 DALYaverted/100PYonART) than for HIV monoinfection, unless ART reduces progression to cirrhosis by more than 70% (33% in base-case).
The additional therapeutic benefits of ART for HBV-related liver disease results in ART generating more health benefits among HBV/HIV-coinfected adults than HIV-monoinfected individuals, whereas less health benefits are generated amongst HCV/HIV coinfection in a generalized HIV epidemic setting.
[show abstract][hide abstract] ABSTRACT: Anna Vassall and colleagues discuss the need for, and challenges facing, innovative and sustainable financing of the HIV response. Please see later in the article for the Editors' Summary.
PLoS Medicine 12/2013; 10(12):e1001567. · 15.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: Antiretroviral therapy (ART) reduces transmission of HIV-1. However, genital HIV-1 can be detected in patients on ART. We analyzed factors associated with genital HIV-1 shedding among high-risk women on ART in Burkina Faso.
Plasma (PVL) and enriched cervico-vaginal lavage HIV-1 RNA were measured every 3-6 months for up to 8 years. Random-effects logistic and linear regression models were used to analyze associations of frequency and quantity of genital HIV-1 RNA with behavioral and biological factors, adjusting for within-woman correlation. The lower limit of detection of HIV-1 RNA in plasma and eCVL samples was 300 copies/ml.
188 participants initiated ART from 2004 to 2011. PVL was detectable in 16% (171/1050) of visits, in 52% (90/174) of women. Cervico-vaginal HIV-1 RNA was detectable in 16% (128/798) of visits with undetectable plasma HIV-1 RNA, in 45% (77/170) of women. After adjusting for PVL, detectable cervico-vaginal HIV-1 RNA was independently associated with abnormal vaginal discharge, and use of nevirapine or zidovudine vs. efavirenz and stavudine respectively; longer time on ART and hormonal contraception were not associated with increased shedding. The presence of bacterial vaginosis, Herpes Simplex Virus-2 (HSV-2) DNA, and the use of nevirapine vs efavirenz were independently associated with an increased quantity of cervico-vaginal HIV-1 RNA.
Certain ART regimens, abnormal vaginal discharge, bacterial vaginosis and genital HSV-2 are associated with HIV-1 cervico-vaginal shedding or quantity in women on ART after adjusting for PVL. This may reduce the effectiveness of ART as prevention in high-risk populations.
[show abstract][hide abstract] ABSTRACT: The UNAIDS Modes of Transmission Model (MoT) is a user-friendly model, developed to predict the distribution of new HIV infections among different subgroups. The model has been used in 29 countries to guide interventions. However, there is the risk that the simplification inherent in the MoT produces misleading findings. Using input data from Nigeria, we compare projections from the MoT with those from a revised model that incorporates additional heterogeneity.
We revised the MoT to explicitly incorporate brothel and street-based sex-work, transactional sex, and HIV-discordant couples. Both models were parameterized using behavioural and epidemiological data from Cross River State, Nigeria. Model projections were compared, and the robustness of the revised model projections to different model assumptions, was investigated.
The original MoT predicts 21% of new infections occur in most-at-risk-populations (MARPs), compared with 45% (40-75%, 95% Crl) once additional heterogeneity and updated parameterization is incorporated. Discordant couples, a subgroup previously not explicitly modelled, are predicted to contribute a third of new HIV infections. In addition, the new findings suggest that women engaging in transactional sex may be an important but previously less recognised risk group, with 16% of infections occurring in this subgroup.
The MoT is an accessible model that can inform intervention priorities. However, the current model may be potentially misleading, with our comparisons in Nigeria suggesting that the model lacks resolution, making it challenging for the user to correctly interpret the nature of the epidemic. Our findings highlight the need for a formal review of the MoT.
AIDS (London, England) 08/2013; · 4.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Background. Interventions such as opiate substitution therapy (OST) and high-coverage needle and syringe
programs (HCNSP) cannot substantially reduce hepatitis C virus (HCV) prevalence among people who inject drugs (PWID). HCV antiviral treatment may prevent onward transmission. We project the impact of combining OST, HCNSP, and antiviral treatment on HCV prevalence/incidence among PWID.
Methods. An HCV transmission model among PWID was used to project the combinations of OST, HCNSP,
and antiviral treatment required to achieve different prevalence and incidence reductions within 10 years for 3
chronic prevalence scenarios and the impact of HCV treatment if only delivered through OST programs. Multivariate and univariate sensitivity analyses were performed.
Results. Large reductions (>45%) in HCV chronic prevalence over 10 years require HCV antiviral treatment.
Scaling up OST and HCNSP substantially reduces the treatment rate required to achieve specific HCV prevalence reductions. If OST and HCNSP coverage were increased to 40% each (no coverage at baseline), then annually treating 10, 23, or 42 per 1000 PWID over 10 years would halve prevalence for 20%, 40%, or 60% baseline chronic HCV prevalences, respectively. Approximately 30% fewer treatments are necessary with new direct-acting antivirals. If coverage of OST and HCNSP is 50% at baseline, similar prevalence reductions require higher treatment rates for the same OST and HCNSP coverage.
Conclusions. Combining antiviral treatment with OST with HCNSP is critical for achieving substantial reductions(>50%) in HCV chronic prevalence over 10 years. Empirical studies are required on how best to scale up antiviraltreatment and combine treatment with other interventions.
[show abstract][hide abstract] ABSTRACT: OBJECTIVE:: Liver disease secondary to hepatitis C virus (HCV) infection in the context of HIV infection is one of the leading non-AIDS causes of death. Sexual transmission of HCV infection among HIV-positive men who have sex with men (MSM) appears to be leading to increased reports of acute HCV infection. Reinfection after successful treatment or spontaneous clearance is reported among HIV-positive MSM but the scale of reinfection is unknown. We calculate and compare HCV reinfection rates among HIV-positive MSM after spontaneous clearance and successful medical treatment of infection. DESIGN:: Retrospective analysis of HIV-positive MSM with sexually acquired HCV who subsequently spontaneously cleared or underwent successful HCV treatment between 2004 and 2012. RESULTS:: Among 191 individuals infected with HCV, 44 were reinfected over 562 person-years of follow-up with an overall reinfection rate of 7.8/100py (95%CI 5.8-10.5). Eight individuals were subsequently reinfected a second time, with a rate of 15.5/100py (95% CI 7.7-31.0). Combining all reinfections, 20% resulted in spontaneous clearance and treatment SVR rates were 73% (16/22) for genotype 1/4 and 100% (2/2) for genotype 2/3.Among 145 individuals with a documented primary infection, the reinfection rate was 8.0 per 100 person-years (95%CI 5.7-11.3) overall, 9.6/100py (95%CI 6.6-14.1) among those successfully treated and 4.2/100py (95%CI 1.7-10.0) among those who spontaneously cleared. The secondary reinfection rate was 23.2/100py (95%CI 11.6-46.4). CONCLUSION:: Despite efforts at reducing risk behaviour, HIV positive MSM who clear HCV infection remain at high risk of reinfection. This emphasizes the need for increased sexual education, surveillance and preventative intervention work.
AIDS (London, England) 06/2013; · 4.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: BACKGROUND: Substantial reductions in HCV prevalence among people who inject drugs (PWID) cannot be achieved by harm reduction interventions such as needle exchange and opiate substitution therapy (OST) alone. Current HCV treatment is arduous and uptake low, but new highly effective and tolerable interferon-free direct-acting antiviral (DAA) treatments could facilitate increased uptake. We projected the potential impact of DAA treatments on PWID HCV prevalence in three settings. METHODS: A dynamic HCV transmission model was parameterized to three chronic HCV prevalence settings: Edinburgh, UK (25%); Melbourne, Australia (50%); Vancouver, Canada (65%). Using realistic scenarios of future DAAs (90% sustained viral response, 12 weeks duration, available 2015), we projected the treatment rates required to reduce chronic HCV prevalence by half or three-quarters within 15 years. RESULTS: Current HCV treatment rates may minimally impact prevalence in Melbourne and Vancouver (<2% relative reductions), but could reduce prevalence by 26% in 15 years in Edinburgh. Prevalence could halve within 15 years with treatment scale-up to 15, 40, or 76 per 1000 PWID annually in Edinburgh, Melbourne, or Vancouver, respectively (2, 13, 15-fold increases, respectively). Scale-up to 22, 54, or 98 per 1000 PWID annually could reduce prevalence by three-quarters within 15 years. Less impact occurs with delayed scale-up, higher baseline prevalence, or shorter average injecting duration. Results are insensitive to risk heterogeneity or restricting treatment to PWID on OST. At existing HCV drug costs, halving chronic prevalence would require annual treatment budgets of USD$3.2 million in Edinburgh and ˜$50 million in Melbourne and Vancouver. CONCLUSION: Interferon-free DAAs could enable increased HCV treatment uptake among PWID, which could have a major preventative impact. However, treatment costs may limit scale-up, and should be addressed. (HEPATOLOGY 2013.).
[show abstract][hide abstract] ABSTRACT: OBJECTIVE:: Estimate the potential impact of Avahan, the India AIDS Initiative, among female sex workers(FSWs) and their clients in five districts of Karnataka state, South India. DESIGN:: Examination of time trends in sexually transmitted infection(STI)/HIV prevalence from serial cross-sectional surveys, combined with mathematical modelling. METHODS:: Survey data from each district were used to monitor changes in FSW STI/HIV prevalence during Avahan. A deterministic model, parameterized with district-specific survey data, was used to simulate HIV/HSV-2/syphilis transmission among high-risk groups in each district. Latin hypercube sampling was used to obtain multiple parameter sets that reproduced district-specific HIV prevalence trends. A Bayesian framework tested whether self-reported increases in consistent condom use(CCU) during Avahan were more compatible with FSW HIV prevalence trends than assuming no or slow (pre-intervention rates) CCU increases, and were used to estimate HIV incidence and infections averted. RESULTS:: Declines in FSW HIV prevalence occurred over 5 years in all districts, and were statistically significant in three. Self-reported increases in CCU were more consistent with observed declines in HIV prevalence in three districts. In all five districts, an estimated 25-64% (32-70%) HIV infections were averted among FSWs (clients) over 5 years. This corresponded to 142-2092 FSW infections averted depending on the district (2-9-fold more among clients). CONCLUSIONS:: Empirical HIV prevalence trends combined with Bayesian modelling has provided plausible evidence that Avahan has reduced HIV transmission among FSWs and their clients. If current CCU levels are sustained, FSW HIV prevalence could decline to low levels by 2015, with many more infections averted.
AIDS (London, England) 03/2013; · 4.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: The hepatitis C virus (HCV) and the human immunodeficiency virus (HIV) are a clear threat for public health, with high prevalences especially in high risk groups such as injecting drug users. People with HIV infection who are also infected by HCV suffer from a more rapid progression to HCV-related liver disease and have an increased risk for cirrhosis and liver cancer. Quantifying the impact of HIV and HCV co-infection is therefore of great importance. We propose a new joint mathematical model accounting for co-infection with the two viruses in the context of injecting drug users (IDUs). Statistical concepts and methods are used to assess the model from a statistical perspective, in order to get further insights in: (i) the comparison and selection of optional model components, (ii) the unknown values of the numerous model parameters, (iii) the parameters to which the model is most 'sensitive' and (iv) the combinations or patterns of values in the high-dimensional parameter space which are most supported by the data. Data from a longitudinal study of heroin users in Italy are used to illustrate the application of the proposed joint model and its statistical assessment. The parameters associated with contact rates (sharing syringes) and the transmission rates per syringe-sharing event are shown to play a major role.
[show abstract][hide abstract] ABSTRACT: BACKGROUND: Amongst injecting drug users (IDUs), HIV is transmitted sexually and parenterally, but HCV is transmitted primarily parenterally. We assess and model the antibody prevalence of HCV amongst HIV-infected IDUs (denoted as HCV-HIV co-infection prevalence) and consider whether it proxies the degree of sexual HIV transmission amongst IDUs. METHODS: HIV, HCV and HCV-HIV co-infection prevalence data amongst IDU was reviewed. An HIV/HCV transmission model was adapted. Multivariate model uncertainty analyses determined whether the model's ability to replicate observed data trends required the inclusion of sexual HIV transmission. The correlation between the model's HCV-HIV co-infection prevalence and estimated proportion of HIV infections due to injecting was evaluated. RESULTS: The median HCV-HIV co-infection prevalence (prevalence of HCV amongst HIV-infected IDUs) was 90% across 195 estimates from 43 countries. High HCV-HIV co-infection prevalences (>80%) occur in most (75%) settings, but can be lower in settings with low HIV prevalence (<10%) or high HIV/HCV prevalence ratios (HIV prevalence divided by HCV prevalence>0.75). The model without sexual HIV transmission reproduced some data trends but could not reproduce any epidemics with high HIV/HCV prevalence ratios (>0.85) or low HCV-HIV co-infection prevalence (<60%) when HIV prevalence>10%. The model with sexual HIV transmission reproduced data trends more closely. The proportion of HIV infections due to injecting correlated with HCV-HIV co-infection prevalence; suggesting that up to 80/60/<20% of HIV infections could be sexually transmitted in settings with HCV-HIV co-infection prevalence between 50-60/70-80/>90%. CONCLUSION: Substantial sexual HIV transmission may occur in many IDU populations; HCV-HIV co-infection prevalence could signify its importance.
Drug and alcohol dependence 02/2013; · 3.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: Syphilis is a major public health problem in many regions of China, with increases in congenital syphilis (CS) cases causing concern. The Chinese Ministry of Health recently announced a comprehensive 10-y national syphilis control plan focusing on averting CS. The decision analytic model presented here quantifies the impact of the planned strategies to determine whether they are likely to meet the goals laid out in the control plan.
Our model incorporated data on age-stratified fertility, female adult syphilis cases, and empirical syphilis transmission rates to estimate the number of CS cases associated with prenatal syphilis infection on a yearly basis. Guangdong Province was the focus of this analysis because of the availability of high-quality demographic and public health data. Each model outcome was simulated 1,000 times to incorporate uncertainty in model inputs. The model was validated using data from a CS intervention program among 477,656 women in China. Sensitivity analyses were performed to identify which variables are likely to be most influential in achieving Chinese and international policy goals. Increasing prenatal screening coverage was the single most effective strategy for reducing CS cases. An incremental increase in prenatal screening from the base case of 57% coverage to 95% coverage was associated with 106 (95% CI: 101, 111) CS cases averted per 100,000 live births (58% decrease). The policy strategies laid out in the national plan led to an outcome that fell short of the target, while a four-pronged comprehensive syphilis control strategy consisting of increased prenatal screening coverage, increased treatment completion, earlier prenatal screening, and improved syphilis test characteristics was associated with 157 (95% CI: 154, 160) CS cases averted per 100,000 live births (85% decrease).
The Chinese national plan provides a strong foundation for syphilis control, but more comprehensive measures that include earlier and more extensive screening are necessary for reaching policy goals. Please see later in the article for the Editors' Summary.
PLoS Medicine 01/2013; 10(1):e1001375. · 15.25 Impact Factor
[show abstract][hide abstract] ABSTRACT: In China, female sex workers (FSWs) are at high risk of syphilis infection, but are hard to reach for interventions. Point-of-care testing introduces opportunities for expanding syphilis control measures. Modelling is used to estimate the impact of using rapid tests to screen FSWs for syphilis. In other settings, modelling has predicted large rebounds in infectious syphilis following screening, which may undermine any impact achieved.
A deterministic syphilis transmission model among FSWs and clients was fitted to data from Yunnan Province (FSW syphilis prevalence = 7.5%), and used to estimate the impact of rapid syphilis testing and treatment for FSWs. Impact projections were compared for different model structures that included risk heterogeneity amongst FSWs, incoming syphilis infections amongst new FSWs and clients and re-infection from FSWs' regular non-commercial partners. The rebound in syphilis prevalence after screening ceased was explored.
All model structures suggest yearly syphilis screening could substantially reduce (by 72-88%) syphilis prevalence amongst FSWs in this setting over five years. However, incoming syphilis infections amongst new FSWs and clients or re-infections from regular non-commercial partners of FSWs can considerably reduce (>30%) the proportion of infections averted. Including heterogeneity in risk amongst FSWs had little effect upon the proportion of infections averted. In this setting, the rebound in syphilis prevalence after screening ceased is predicted to be slight, but it could be large in high prevalence settings.
Rapid test screening could dramatically reduce syphilis prevalence amongst hard-to-reach groups, but strategies to reduce re-infection from regular non-commercial partners are needed to maximise impact.
PLoS ONE 01/2013; 8(1):e55622. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: People who inject drugs (PWID) are at high risk for acquiring hepatitis C virus (HCV), but many are unaware of their infection. HCV dried blood spot (DBS) testing increases case-finding in addiction services and prisons. We determine the cost-effectiveness of increasing HCV case-finding among PWID by offering DBS testing in specialist addiction services or prisons as compared to using venepuncture.
Cost-utility analysis using a dynamic HCV transmission model among PWID, including: disease progression, diagnosis, treatment, injecting status, incarceration and addition services contact.
DBS testing in specialist addiction services or prisons. Intervention impact was determined by a meta-analysis of primary data.
Costs (in UK £, £1=US$1.60) and utilities (quality-adjusted life years, QALYs) were attached to each state and the incremental cost effectiveness ratio (ICER) determined. Multivariate uncertainty and one-way sensitivity analyses were performed.
For a £20 000 per QALY gained willingness-to-pay threshold, DBS testing in addiction services is cost-effective (ICER of £14 600 per QALY gained). Under the base-case assumption of no continuity of treatment/care when exiting/entering prison, DBS testing in prisons is not cost-effective (ICER of £59 400 per QALY gained). Results are robust to changes in HCV prevalence; increasing PWID treatment rates to those for ex-PWID considerably reduces ICER (£4500 and £30 000 per QALY gained for addiction services and prison, respectively). If continuity of care is >40%, the prison DBS ICER falls below £20 000 per QALY gained.
Despite low PWID treatment rates, increasing case-finding can be cost-effective in specialist addiction services, and in prisons if continuity of treatment/care is ensured.
[show abstract][hide abstract] ABSTRACT: For the first time in the history of HIV, new bio-medical interventions have been shown to be effective in preventing HIV transmission. For these new HIV prevention technologies (NPTs) to have an impact on the epidemic, they must be widely used. This study uses a discrete choice experiment (DCE) to: understand the relative strength of women's preferences for product characteristics, understand the implications for substitution away from male condoms, and inform realistic modelling of their potential impact and cost-effectiveness.
A DCE was conducted among 1017 women in urban South Africa. Women were presented with choices between potential women's NPTs (microbicides, diaphragm, female condom) and 'what I did last time' (use or not use a condom) with different HIV and pregnancy prevention effectiveness' and prices. Choice probabilities are estimated using the nested logit model and used to predict uptake.
In this high HIV prevalence setting, HIV prevention effectiveness is the main driver of uptake followed by pregnancy prevention effectiveness. For example a microbicide with poor effectiveness would have niche appeal at just 11% predicted uptake, while a highly effective microbicide (95% effective against HIV and pregnancy) would have far wider appeal (56% predicted uptake). Though women who reported not using condoms were more likely to choose the NPTs, at current very high rates of male condom use in South Africa (60%), about half of microbicide uptake is projected to be among those currently not using condoms.
Women are very interested in NPTs, especially if highly effective in preventing HIV and pregnancy. Women in greatest need were also most likely to switch to the new products. Where products are not yet available for distribution, proxy data, such as that generated by DCEs, can bring realism to overly optimistic uptake scenarios found in many current impact models.
PLoS ONE 01/2013; 8(12):e83193. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Evaluation of HIV large scale interventions programme is becoming
increasingly important, but impact estimates frequently hinge on knowledge of
changes in behaviour such as the frequency of condom use (CU) 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 a dynamic HIV transmission dynamics model to estimate CU 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 CU is critical in the context studied, due to the very
limited amount of CU and HIV data available We consider various novel
formulations to explore the trajectory of CU in time, based on diffusion-driven
trajectories and smooth sigmoid curves. Extensive series of numerical
simulations indicate that informative results can be obtained regarding the
amplitude of the increase in CU 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 illustrates how it can help
evaluate HIV intervention from few observational studies and suggests that
these methods can potentially be applied in many different contexts.