Heterosexual Anal Intercourse Has the Potential to Cause a Significant Loss of Power in Vaginal Microbicide Effectiveness Studies

Understanding the sources of efficacy dilution in a trial of a monthly dapivirine vaginal ring for HIV-1 prevention

INTRODUCTION

Women-initiated HIV - 1 prevention products are key to reducing women's HIV-1 risk. Clinical trials of vaginal microbicides have shown limited to no efficacy in intention-to-treat (ITT) analyses. It is hypothesized that these negative results are partly due to efficacy dilution.

METHODS

We developed a microsimulation model of MTN-020/ASPIRE, a phase 3 trial that evaluated monthly use of a dapivirine vaginal ring for HIV-1 prevention. We evaluated four sources of efficacy dilution: trial-level factors: (i) an imbalance in the number of monthly sex acts between study arms and (ii) heterogeneity in risk emergent over time; and individual-level factors: (iii) product non-adherence and (iv) receptive anal intercourse.

RESULTS

Assuming 70% per-vaginal exposure efficacy (consistent with the ITT estimate of 27%), heterogeneity in risk accounted for the largest proportion of efficacy dilution, at 42% (90% CrI: 38, 45), followed by non-adherence (33%; 90% CrI: 27, 39), an imbalance in arms (18%; 90% CrI: 16, 21) and lastly, anal intercourse with less than 10% of efficacy dilution.

CONCLUSION

Our results suggest that heterogeneity in risk was the most important source of efficacy dilution in the ASPIRE trial. Future trials of HIV-1 prevention products for women should consider alternative trial designs and analytic approaches that minimize bias introduced by heterogeneity in risk.

The Association Between Heterosexual anal Intercourse and HIV Acquisition in Three Prospective Cohorts of Women

The extent to which receptive anal intercourse (RAI) increases the HIV acquisition risk of women compared to receptive vaginal intercourse (RVI) is poorly understood. We evaluated RAI practice over time and its association with HIV incidence during three prospective HIV cohorts of women: RV217, MTN-003 (VOICE), and HVTN 907. At baseline, 16% (RV 217), 18% (VOICE) of women reported RAI in the past 3 months and 27% (HVTN 907) in the past 6 months, with RAI declining during follow-up by around 3-fold. HIV incidence in the three cohorts was positively associated with reporting RAI at baseline, albeit not always significantly. The adjusted hazard rate ratios for potential confounders (aHR) were 1.1 (95% Confidence interval: 0.8-1.5) for VOICE and 3.3 (1.6-6.8) for RV 217, whereas the ratio of cumulative HIV incidence by RAI practice was 1.9 (0.6-6.0) for HVTN 907. For VOICE, the estimated magnitude of association increased slightly when using a time-varying RAI exposure definition (aHR = 1.2; 0.9-1.6), and for women reporting RAI at every follow-up survey (aHR = 2.0 (1.3-3.1)), though not for women reporting higher RAI frequency (> 30% acts being RAI vs. no RAI in the past 3 months; aHR = 0.7 (0.4-1.1)). Findings indicated precise estimation of the RAI/HIV association, following multiple RVI/RAI exposures, is sensitive to RAI exposure definition, which remain imperfectly measured. Information on RAI practices, RAI/RVI frequency, and condom use should be more systematically and precisely recorded and reported in studies looking at sexual behaviors and HIV seroconversions; standardized measures would aid comparability across geographies and over time.

The Impact of Ingroup and Outgroup Exclusion on HIV-Risk Cognitions in Sexual Minority Men

BACKGROUND

Sexual minority men (SMM) face disproportionate rates of HIV/AIDS. Emerging evidence indicates that minority stress (e.g., discrimination) and stress from within the gay community itself (e.g., exclusion) may contribute to sexual orientation disparities in HIV prevalence and risk.

PURPOSE

This study investigated the impact of sexual orientation discrimination and exclusion by the gay community on SMM's intentions to engage in HIV-risk behavior.

METHODS

We conducted an experiment in which we employed an exclusion manipulation to induce (a) perceived discrimination from the outgroup and (b) perceived exclusion by the ingroup in a community sample of 194 SMM. Participants completed a baseline assessment of previous discrimination, exposure to gay community stress, and HIV-risk behavior. Two days later, participants completed an experiment in which they were randomized to one of four conditions in the game Cyberball: (a) exclusion by straight men, (b) inclusion by straight men, (c) exclusion by gay men, or (d) inclusion by gay men. Risky sex intentions were then assessed.

RESULTS

Discrimination and gay community stress were positively associated with HIV-risk behaviors at baseline. Participants who were excluded (vs. included) by straight men in the experimental task reported more risky sex intentions. This effect was mediated by decreases in state self-esteem. Risky sex intentions did not differ between participants who were included versus excluded by gay men.

CONCLUSIONS

This study provides the first experimental evidence that discrimination is associated with sexual risk taking in SMM, and elucidates a potential psychological mechanism through which this effect operates.

Women for science and science for women: Gaps, challenges and opportunities towards optimizing pre-exposure prophylaxis for HIV-1 prevention

Preventing new HIV infections remains a global challenge. Young women continue to bear a disproportionate burden of infection. Oral pre-exposure prophylaxis (PrEP), offers a novel women-initiated prevention technology and PrEP trials completed to date underscore the importance of their inclusion early in trials evaluating new HIV PrEP technologies. Data from completed topical and systemic PrEP trials highlight the role of gender specific physiological and social factors that impact PrEP uptake, adherence and efficacy. Here we review the past and current developments of HIV-1 prevention options for women with special focus on PrEP considering the diverse factors that can impact PrEP efficacy. Furthermore, we highlight the importance of inclusion of female scientists, clinicians, and community advocates in scientific efforts to further improve HIV prevention strategies.

Acceptability of the Dapivirine Vaginal Ring in Postmenopausal US Women

For women in the United States who remain sexually active beyond child-bearing years, susceptibility to HIV infection remains, yet condom use is low. We assessed acceptability of the dapivirine vaginal ring (ring) among 96 postmenopausal US women enrolled in a placebo-controlled multisite phase II trial of the ring, using questionnaires and in-depth interviews. Three quarters of women reported “perfect” adherence (ring never out) over the 3-month trial period. At study exit, the ring was found to be very easy to use by 72%, very comfortable to wear by 65%, and 4% reported it ever interfered with their daily activities. The most common worries among participants at preinitiation had decreased significantly at study exit (e.g., worries about inserting the ring declined from 46% to 6%, discomfort during daily activities from 53% to 3%, ring not staying in place from 48% to 14%, all p < 0.0001). Despite some couples feeling the ring during sex, the ring was perceived as more suitable than condoms for prevention because it was not burdensome to use, did not interfere with erection, and provided (for some) additional vaginal lubrication. The ring is a promising, highly acceptable HIV prevention method that is suitable to the lives of postmenopausal women and their male partners and can provide them with an additional prevention choice.

Clinical Trials Registration: NCT02010593.

Application of a Body Map Tool to Enhance Discussion of Sexual Behavior in Women in South Africa, Uganda, and Zimbabwe

Body mapping methods are used in sexual and reproductive health studies to encourage candid discussion of sex and sexuality, pleasure and pain, sickness and health, and to understand individuals' perceptions of their bodies. VOICE-D, a qualitative follow-up study to the VOICE trial, developed and used a body map tool in the context of individual in-depth interviews with women in South Africa, Uganda, and Zimbabwe. The tool showed the outline of a nude female figure from the front and back perspective. We asked women to identify, label, and discuss genitalia and other body parts associated with sexual behaviors, pain, and pleasure. Respondents could indicate body parts without having to verbalize potentially embarrassing anatomical terms, enabling interviewers to clarify ambiguous terminology that may have otherwise been open to misinterpretation. Body maps provided women with a non-intimidating way of discussing and disclosing their sexual practices, and minimized miscommunication of anatomical and behavioral terminology.

Increases in HIV Incidence Following Receptive Anal Intercourse Among Women: A Systematic Review and Meta-analysis

Receptive anal intercourse (RAI) carries a greater per-act risk of HIV acquisition than receptive vaginal intercourse (RVI) and may influence HIV epidemics driven by heterosexual sex. This systematic review explores the association between RAI and incident HIV among women, globally. We searched Embase and Medline through September 2018 for longitudinal studies reporting crude (cRR) or adjusted (aRR) relative risks of HIV acquisition by RAI practice among women. Of 27,563 articles identified, 17 eligible studies were included. We pooled independent study estimates using random-effects models. Women reporting RAI were more likely to acquire HIV than women not reporting RAI (pooled cRR = 1.56 95% CI 1.03–2.38, N = 18, I² = 72%; pooled aRR = 2.23, 1.01–4.92, N = 5, I² = 70%). In subgroup analyses the association was lower for women in Africa (pooled cRR = 1.16, N = 13, I² = 21%) than outside Africa (pooled cRR = 4.10, N = 5, I² = 79%) and for high-risk (pooled aRR = 1.69, N = 4, I² = 63%) than general-risk women (pooled aRR = 8.50, N = 1). Interview method slightly influenced cRR estimates (p value = 0.04). In leave-one-out sensitivity analyses pooled estimates were generally robust to removing individual study estimates. Main limitations included poor exposure definition, incomplete adjustment for confounders, particularly condom use, and use of non-confidential interview methods. More and better data are needed to explain differences in risk by world region and risk population. Women require better counselling and greater choice in prevention modalities that are effective during RVI and RAI.

In Vivo Modulation of Cervicovaginal Drug Transporters and Tissue Distribution by Film-Released Tenofovir and Darunavir for Topical Prevention of HIV-1

Clinical trials have demonstrated partial protection against HIV-1 infection by vaginal microbicide formulations based on antiretroviral (ARV) drugs. Improved formulations that will maintain sustained drug concentrations at viral target sites in the cervicovaginal mucosa are needed. We have previously demonstrated that treatment of cervicovaginal cell lines with ARV drugs can alter gene expression of drug transporters, suggesting that the mucosal disposition of ARV drugs delivered vaginally can be modulated by drug transporters. This study aimed to investigate in vivo modulation of drug transporter expression in a nonhuman primate model by tenofovir and darunavir released from film formulations. Cervicovaginal tissues were collected from drug-naïve macaques and from macaques vaginally treated with film formulations of tenofovir or darunavir. Drug release in vaginal fluid as well as drug absorption in cervicovaginal tissues and lymph nodes were verified by mass spectrometry. The effects of exposure to drugs on the expression of transporters relevant to ARV drugs were evaluated by quantitative PCR. We showed expression in cervicovaginal tissue of drug-naïve macaques of transporters important for distribution of ARV drugs, albeit at lower levels compared to human tissue for key transporters including P-glycoprotein. Concentrations of tenofovir and darunavir well above the EC₅₀ values determined in vitro were detected in vaginal fluid and vaginal tissues of macaques treated with drug-dissolving films over 24 h and were also comparable to those shown previously to modulate drug transporter expression. Accordingly, Multidrug Resistance associated Protein 2 (MRP2) in cervicovaginal tissue was upregulated by both tenofovir and darunavir. The two drugs also differentially induced and/or inhibited expression of key uptake transporters for reverse transcriptase inhibitors and protease inhibitors. The lower expression of key transporters in macaques may result in increased retention of ARV drugs at the simian cervicovaginal mucosa compared to the human mucosa and has implications for translation of preclinical data. Modulation of drug transporter expression by tenofovir and darunavir points to the potential benefit of MRP2 inhibition to increase ARV drug penetration through the cervicovaginal epithelium.

Prevalence and correlates of anal intercourse among female sex workers in eSwatini

INTRODUCTION

As HIV is very effectively acquired during condomless receptive anal intercourse (AI) with serodiscordant and viremic partners, the practice could contribute to the high prevalence among female sex workers (FSW) in eSwatini (formerly known as Swaziland). We aim to estimate the proportion reporting AI (AI prevalence) among Swazi FSW and to identify the correlates of AI practice in order to better inform HIV prevention interventions among this population.

METHODS

Using respondent-driven sampling (RDS), 325 Swazi FSW were recruited in 2011. We estimated the prevalence of AI and AI with inconsistent condom use in the past month with any partner type, and inconsistent condom use during AI and vaginal intercourse (VI) by partner type. Univariate and multivariable logistic regression models were used to identify behavioural and structural correlates associated with AI and AI with inconsistent condom use.

RESULTS

RDS-adjusted prevalence of AI and AI with inconsistent condom use was high, at 44%[95% confidence interval (95%CI):35-53%]) and 34%[95%CI:26-42%], respectively and did not vary by partner type. HIV prevalence was high in this sample of FSW (70%), but knowledge that AI increases HIV acquisition risk low, with only 10% identifying AI as the riskiest sex act. Those who reported AI were more likely to be better educated (adjusted odds ratio(aOR) = 1.92[95%CI:1.03-3.57]), to have grown up in rural areas (aOR = 1.90[95%CI:1.09-3.32]), have fewer new clients in the past month (aOR = 0.33[95%CI:0.16-0.68]), and for last sex with clients to be condomless (aOR = 2.09[95%CI:1.07-4.08]). Although FSW reporting AI in past month were more likely to have been raped (aOR = 1.95[95%CI:1.05-3.65]) and harassed because of being a sex worker (aOR = 2.09[95%CI:1.16-3.74]), they were also less likely to have ever been blackmailed (aOR = 0.50[95%CI:0.25-0.98]) or been afraid to walk in public places (aOR = 0.46[95%CI:0.25-0.87]). Correlates of AI with inconsistent condom use were similar to those of AI.

CONCLUSIONS

AI is commonly practised and condom use is inconsistent among Swazi FSW. Sex act data are needed to determine how frequently AI is practiced. Interventions to address barriers to condom use are needed, as are biomedical interventions that reduce acquisition risk during AI.

Efficacy of Vaginally Administered Gel Containing Emtricitabine and Tenofovir Against Repeated Rectal Simian Human Immunodeficiency Virus Exposures in Macaques

Vaginal microbicides containing antiretrovirals (ARVs) have shown to prevent vaginally acquired human immunodeficiency virus (HIV), but these products may not protect women who engage in anal sex. Intravaginal dosing with ARVs has shown to result in drug exposures in rectal tissues, thus raising the possibility of dual compartment protection. To test this concept, we investigated whether intravaginal dosing with emtricitabine (FTC)/tenofovir (TFV) gel, which fully protected macaques against repeated vaginal exposures to simian human immunodeficiency virus (SHIV), protects against rectal SHIV exposures. Pharmacokinetic studies revealed rapid distribution of FTC and TFV to rectal tissues and luminal fluids, albeit at concentrations 1-2 log10 lower than those in the vaginal compartment. Efficacy measurements against repeated rectal SHIV challenges demonstrated a 4.5-fold reduction in risk of infection in macaques that received intravaginal FTC/TFV compared to placebo gel (P = .047; log-rank test). These data support the concept of dual compartment protection by vaginal dosing and warrants developing ARV-based vaginal products with improved bidirectional dosing.

Effects of gel volume on pharmacokinetics for vaginal and rectal applications of combination DuoGel-IQB4012, a dual chamber-dual drug HIV microbicide gel, in pigtailed macaques

This study evaluated effects of differing gel volumes on pharmacokinetics (PK). IQB4012, a gel containing the non-nucleoside reverse transcriptase inhibitor IQP-0528 and tenofovir (TFV), was applied to the pigtailed macaque vagina and rectum. Vaginal gel volumes (1% loading of both drugs) were 0.5 or 1.5 ml; following wash-out, 1 or 4 ml of gel were then applied rectally. Blood, vaginal, and rectal fluids were collected at 0, 2, 4, and 24 h. Vaginal and rectal tissue biopsies were collected at 4 and 24 h. There were no statistically significant differences in concentrations for either drug between gel volumes within compartments at matched time points. After vaginal gel application, median IQP-0528 concentrations were ~ 10⁴-10⁵ ng/g, 10⁵-10⁶ ng/ml, and 10³-10⁵ ng/ml in vaginal tissues, vaginal fluids, and rectal fluids, respectively (over 24 h). Median vaginal TFV concentrations were 1-2 logs lower than IQP-0528 levels at matched time points. After rectal gel application, median IQP-0528 and TFV concentrations in rectal fluids were ~ 10³-10⁵ ng/ml and ~ 10²-10³ ng/ml, respectively. Concentrations of both drugs sampled in rectal tissues were low (~ 10¹-10³ ng/g). For 1 ml gel, half of sampled rectal tissues had undetectable concentrations of either drug, and over half of sampled rectal fluids had undetectable TFV concentrations. These results indicate differences in drug delivery between the vaginal and rectal compartments, and that smaller vaginal gel volumes may not significantly compromise microbicide PK and prophylactic potential. However, effects of rectal gel volume on PK for both drugs were less definitive.

How common and frequent is heterosexual anal intercourse among South Africans? A systematic review and meta-analysis

BACKGROUND

HIV is transmitted more effectively during anal intercourse (AI) than vaginal intercourse (VI). However, patterns of heterosexual AI practice and its contribution to South Africa's generalized epidemic remain unclear. We aimed to determine how common and frequent heterosexual AI is in South Africa.

METHODS

We searched for studies reporting the proportion practising heterosexual AI (prevalence) and/or the number of AI and unprotected AI (UAI) acts (frequency) in South Africa from 1990 to 2015. Stratified random-effects meta-analysis by sub-groups was used to produce pooled estimates and assess the influence of participant and study characteristics on AI prevalence. We also estimated the fraction of all sex acts which were AI or UAI and compared condom use during VI and AI.

RESULTS

Of 41 included studies, 31 reported on AI prevalence and 14 on frequency, over various recall periods. AI prevalence was high across different recall periods for sexually active general-risk populations (e.g. lifetime = 18.4% [95%CI:9.4-27.5%], three-month = 20.3% [6.1-34.7%]), but tended to be even higher in higher-risk populations such as STI patients and female sex workers (e.g. lifetime = 23.2% [0.0-47.4%], recall period not stated = 40.1% [36.2-44.0%]). Prevalence was higher in studies using more confidential interview methods. Among general and higher-risk populations, 1.2-40.0% and 0.7-21.0% of all unprotected sex acts were UAI, respectively. AI acts were as likely to be condom protected as vaginal acts.

CONCLUSION

Reported heterosexual AI is common but variable among South Africans. Nationally and regionally representative sexual behaviour studies that use standardized recall periods and confidential interview methods, to aid comparison across studies and minimize reporting bias, are needed. Such data could be used to estimate the extent to which AI contributes to South Africa's HIV epidemic.

Condoms, Lubricants and Rectal Cleansing: Practices Associated with Heterosexual Penile-Anal Intercourse Amongst Participants in an HIV Prevention Trial in South Africa, Uganda and Zimbabwe

We investigated condom and lubricant use, rectal cleansing and rectal gel use for penile-anal intercourse (PAI), during in-depth interviews with women from South Africa, Uganda and Zimbabwe who formerly participated in VOICE, a five-arm HIV prevention trial of two antiretroviral tablets and a vaginal gel. Few studies have addressed practices related to PAI among women; existing data from Africa on condom and lubricant use for PAI, as well as preparatory practices of PAI such as rectal cleansing, are limited to men who have sex with men. Women demonstrated a lack of awareness of HIV transmission risks of PAI and none of the participants reported using condom-compatible lubricants for PAI. Participants described a variety of preparatory rectal cleansing practices. Some participants disclosed rectal use of the vaginal study gel. Understanding practices related to PAI in Africa is critical to microbicide development, as these practices are likely to influence the acceptability, feasibility, and use of both vaginal and rectal microbicide products.

'HIV has a woman's face': vaginal microbicides and a case of ambiguous failure

The case is a primary unit of knowledge production in the field of HIV research, yet the work that is done to construct cases often goes unremarked. In this paper, the case takes centre stage in an analysis of a set of apparent failures in HIV prevention research, namely a series of clinical trials to test vaginal microbicides. Returning to the genesis of the microbicide concept in the early 1990s, I examine how the discourse of women's empowerment was linked to HIV prevention in a way that mobilized a particular vision of the case, which was both politically and scientifically expedient. Drawing on an in-depth empirical study of one particular trial, I show the success of the case in mobilizing funds and interest in the research, as well its success in accounting for the failure of the pharmaceutical technology. Drawing in alternative scientific accounts of the failure of microbicides, however, a different version of events is indicated, in which what can ultimately be said to have failed is not the technology itself, but the act of casing upon which its testing was founded.

Prevalence and Frequency of Heterosexual Anal Intercourse Among Young People: A Systematic Review and Meta-analysis

We aim to assess if heterosexual anal intercourse (AI) is commonly practiced and how frequently it is practiced by young people. We searched PubMed for articles published 1975 to July 2014 reporting data on the proportion of young people (mean age <25) practicing heterosexual AI (AI prevalence) and on number of AI acts (AI frequency). Stratified random-effects meta-analysis and meta-regression were used to produce summary estimates and assess the influence of participant and study characteristics on AI prevalence. Eighty-three and thirteen of the 136 included articles reported data on lifetime AI prevalence and monthly AI frequency, respectively. Estimates were heterogenous. Overall summary estimates of lifetime AI prevalence were 22 % (95 % confidence interval 20-24) among sexually active young people, with no statistically significant differences by gender, continent or age. Prevalence increased significantly with confidentiality of interview method and, among males and in Europe, by survey year. Prevalence did not significantly differ by recall period. An estimated 3-24 % of all reported sex acts were AI. Reported heterosexual AI is common but variable among young people worldwide. To fully understand its impact on STI spread, more and better quality data on frequency of unprotected AI, and trends over time are required.

Rectal microbicide development

The last few years have seen important progress in demonstrating the efficacy of oral pre-exposure prophylaxis, vaginal microbicides, and treatment as prevention as effective strategies for reducing the risk of acquiring or transmitting HIV infection. There has also been significant progress in the development of rectal microbicides. Preclinical non-human primate studies have demonstrated that antiretroviral microbicides can provide significant protection from rectal challenge with SIV or SHIV. Recent Phase 1 rectal microbicide studies have characterized the safety, acceptability, compartmental pharmacokinetics (PK), and pharmacodynamics (PD) of both UC781 and tenofovir gels. The tenofovir gel formulation used in vaginal studies was not well tolerated in the rectum and newer rectal-specific formulations have been developed and evaluated in Phase 1 studies. The PK/PD data generated in these Phase 1 studies may reduce the risk of advancing ineffective candidate rectal microbicides into late stage development. Tenofovir gel is currently poised to move into Phase 2 evaluation and it is possible that a Phase 2B/3 effectiveness study with this product could be initiated in the next 2-3 years.

Comprehensive assessment of HIV target cells in the distal human gut suggests increasing HIV susceptibility toward the anus

BACKGROUND

Prevention of rectal HIV transmission is a high-priority goal for vaccines and topical microbicides because a large fraction of HIV transmissions occurs rectally. Yet, little is known about the specific target-cell milieu in the human rectum other than inferences made from the colon.

METHODS

We conducted a comprehensive comparative in situ fluorescence study of HIV target cells (CCR5-expressing T cells, macrophages, and putative dendritic cells) at 4 and 30 cm proximal of the anal canal in 29 healthy individuals, using computerized analysis of digitized combination stains.

RESULTS

Most strikingly, we find that more than 3 times as many CD68 macrophages express the HIV coreceptor CCR5 in the rectum than in the colon (P = 0.0001), and as such rectal macrophages seem biologically closer to the HIV-susceptible CCR5 phenotype in the vagina than the mostly HIV-resistant CCR5 phenotype in the colon. Putative CD209 dendritic cells are generally enriched in the colon compared with the rectum (P = 0.0004), though their CCR5 expression levels are similar in both compartments. CD3 T-cell densities and CCR5 expression levels are comparable in the colon and rectum.

CONCLUSIONS

Our study establishes the target-cell environment for HIV infection in the human distal gut and demonstrates in general terms that the colon and rectum are immunologically distinct anatomical compartments. Greater expression of CCR5 on rectal macrophages suggests that the most distal sections of the gut may be especially vulnerable to HIV infection. Our findings also emphasize that caution should be exercised when extrapolating data obtained from colon tissues to the rectum.

Effect of computer-assisted interviewing on self-reported sexual behavior data in a microbicide clinical trial

In a microbicide safety and effectiveness trial (HPTN 035) in Malawi, 585 women completed the same questionnaire through a face-to-face interview (FTFI) and an audio computer-assisted self-interview (ACASI). Concordance between FTFI and ACASI responses ranged from 72.0 % for frequency of sex in the past week to 95.2 % for anal intercourse (AI) in the past 3 months. Reported gel and condom use at last sex act were marginally lower with ACASI than FTFI (73.5 % vs. 77.2 %, p = 0.11 and 60.9 % vs. 65.5 %, p = 0.05, respectively). More women reported AI with ACASI than FTFI (5.0 % vs. 0.2 %, p < 0.001). Analyses of consistency of responses within ACASI revealed that 15.0 % of participants in the condom-only arm and 28.7 % in the gel arm provided at least one discrepant answer regarding total sex acts and sex acts where condom and gel were used (19.2 % reported one inconsistent answer, 8.1 % reported two inconsistent answers, and 1.4 % reported three inconsistent answers). While ACASI may provide more accurate assessments of sensitive behaviors in HIV prevention trials, it also results in a high level of internally inconsistent responses.

A comparison of sexual behavior patterns among men who have sex with men and heterosexual men and women

OBJECTIVE

Men who have sex with men (MSM) have higher rates of HIV and other sexually transmitted infections than women and heterosexual men. This elevated risk persists across age groups and reflects biological and behavioral factors; yet, there have been few direct comparisons of sexual behavior patterns between these populations.

METHODS

We compared sexual behavior patterns of MSM and male and female heterosexuals aged 18-39 using 4 population-based random digit dialing surveys. A 1996-1998 survey in 4 US cities and 2 Seattle surveys (2003 and 2006) provided estimates for MSM; a 2003-2004 Seattle survey provided data about heterosexual men and women.

RESULTS

Sexual debut occurred earlier among MSM than heterosexuals. MSM reported longer cumulative lifetime periods of new partner acquisition than heterosexuals and a more gradual decline in new partnership formation with age. Among MSM, 86% of 18- to 24-year-olds and 72% of 35- to 39-year-olds formed a new partnership during the previous year, compared with 56% of heterosexual men and 34% of women at 18-24 years, and 21% and 10%, respectively, at 35-39 years. MSM were also more likely to choose partners >5 years older and were 2-3 times as likely as heterosexuals to report recent concurrent partnerships. MSM reported more consistent condom use during anal sex than heterosexuals reported during vaginal sex.

CONCLUSIONS

MSM have longer periods of partnership acquisition, a higher prevalence of partnership concurrency, and more age disassortative mixing than heterosexuals. These factors likely help to explain higher HIV/sexually transmitted infections rates among MSM, despite higher levels of condom use.

Comparison of sexual behavior and HIV risk between two HIV-1 serodiscordant couple cohorts: the CHAVI 002 study

BACKGROUND

The CHAVI002 study was designed to characterize immune responses, particularly HIV-specific T-cell responses, amongst 2 cohorts of HIV-exposed seronegative (HESN) individuals. The absence of a clear definition of HESNs has impaired comparison of research within and between such cohorts. This report describes two distinct HESN cohorts and attempts to quantify HIV exposure using a 'HIV risk index' (RI) model.

METHODS

HIV serodiscordant couples (UK; 24, Uganda; 72) and HIV unexposed seronegative (HUSN) controls (UK; 14, Uganda; 26 couples, 3 individuals) completed sexual behavior questionnaires every 3 months over a 9 month period. The two cohorts were heterogeneous, with most HESNs in the UK men who have sex with men (MSM), while all HESNs in Uganda were in heterosexual relationships. Concordance of responses between partners was determined. Each participant's sexual behavior score (SBS) was estimated based on the number and type of unprotected sex acts carried out in defined time periods. Independent HIV acquisition risk factors (partner plasma viral load, STIs, male circumcision, pregnancy) were integrated with the SBS, generating a RI for each HESN.

RESULTS

96 HIV serodiscordant couples completed 929 SBQs. SBSs remained relatively stable amongst the UK cohort, whilst decreasing from Visit 1 to 2 in the Ugandan cohort. Compared to the Ugandan cohort, SBSs and RIs in the UK cohort were lower at visit 1, and generally higher at later visits. Differences between the cohorts, with lower rates of ART use in Uganda and higher risk per-act sex in the UK, had major impacts on the SBSs and RIs of each cohort. There was one HIV transmission event in the UK cohort.

CONCLUSIONS

Employment of a risk quantification model facilitated quantification and comparison of HIV acquisition risk across two disparate HIV serodiscordant couple cohorts.

An adaptive design to bridge the gap between Phase 2b/3 microbicide effectiveness trials and evidence required for licensure

Background

Vaginally and rectally applied microbicides are being developed to help prevent sexual acquisition of HIV. Due to the lack of surrogate outcomes, the path toward licensure typically moves directly from expanded safety studies to expensive Phase 2b/3 trials with rare incident infection outcomes. The need to confirm an initial trial’s significant finding can lead to serious delays in implementing essential programs to reduce the spread of HIV.

Purpose

To propose an adaptive design where a Phase 2b/3 study powered to detect a clinically meaningful effect with evidence of one trial (observing one-sided p < 0.025) is allowed to expand by a prespecified, feasible amount if interim data suggest the chance of further achieving a more robust evidence threshold ( p < 0.001, potentially sufficient for licensure from a single trial) is promising.

Methods

As an example, prespecified conditional power criteria are used to determine whether a 90-event trial with 90% power to detect a 50% reduction in risk should be expanded to 130 events. Asymptotic results and simulations are used to assess false-positive error rates and other operating characteristics of the design.

Results

False-positive error rates can be controlled at the desired 0.025 and 0.001 levels with appropriate choice of critical values or expansion criteria. The chance of achieving robust evidence can approach that of a 130-event trial with traditional stopping boundaries (controlling a = 0.001) but with substantially lower expected size for plausible effectiveness levels.

Limitations

Conditional power calculations assume the interim estimate of effect is an unbiased estimate for the remainder of the trial, an assumption which may not hold if product adherence varies over time. Observing a measure of effect with p < 0.001 may not be sufficient for licensure. A decision to expand the trial would be informative to investigators regarding the interim effect size.

Conclusions

A moderate increase in trial size can make the difference between a study with good power to detect a clinically meaningful effect and one which may reasonably obtain the robust evidence required for regulatory bodies and public health programs to consider making a new microbicide available to persons at risk of HIV infection. The proposed design allows for this possibility while not requiring investigators to make an up-front commitment to a prohibitively large trial.

Statistical and methodological issues in microbicide trial design

Microbicide trials aim to measure the effect of a microbicide in reducing the risk of acquiring human immunodeficiency virus. Such trials present a number of challenging issues from design and conduct through to analysis and reporting. This begins with the initial identification of the target trial population. Prevention trials need to identify those at risk of human immunodeficiency virus infection. This can be more difficult in the general population compared with treatment trials that can target specific patient groups who have a confirmed diagnosis of the disease of interest. Consequently, microbicide trial participants will inevitably be recruited who are never at risk of HIV infection. In this chapter we outline the main features of microbicide trial design, key issues during conduct and analysis, and discuss the challenges specific to these types of clinical trials.

Anal sex, vaginal practices, and HIV incidence in female sex workers in urban Kenya: implications for the development of intravaginal HIV prevention methods

Multiple intravaginal HIV prevention methods, including microbicide gels, barriers, and intravaginal rings, are in clinical development in Africa. Development of intravaginal HIV prevention products requires an understanding of sexual behavior, sexually transmitted infection (STI), and vaginitis prevalences, and sexual and vaginal practices in potential target populations. We assessed these factors in a cohort of Kenyan female sex workers (FSW). Women who reported exchanging sex for money/gifts at least three times in the past month and who were HIV uninfected were enrolled and followed for 6 months. STI prevalence and HIV incidence were analyzed by multivariate logistic regression analysis, controlling for demographic and behavioral factors. Thirty-seven percent (74/200) reported having had anal sex. Frequency of anal sex was higher with regular and casual partners than with primary partners. Women were less likely to use condoms for anal sex than for vaginal sex with regular or casual partners. Vaginal washing was universal (100%). HIV incidence was 5.6 per 100 person-years (95% CI 1.62, 11.67). HIV incidence was not associated with any demographic or risk behavior. The relatively high rate of anal sex and universal vaginal washing may complicate both safety and efficacy evaluation of intravaginal products and should be taken into account in trial design. This FSW population had significant HIV incidence and needs continued HIV prevention interventions.

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.

Notes on the frequency of routinely collected and self-reported behavioral data in HIV prevention trials

HIV prevention trials typically randomize thousands of participants to active or control intervention arms, with regular (e.g. monthly) clinic visits over one or more years of follow-up. Because HIV infection rates are often lower than 3 per 100 person-years even in high prevalence settings, tens of thousands of clinic visits may take place before the number of infections required to achieve adequate study power has been observed. In addition to clinical outcomes, the multitude of study visits provides an opportunity to assess adherence and related participant behaviors in great detail. These data may be used to refine counseling messages, gain insight into patterns of behavior, and perform supporting analyses in an attempt to obtain more precise estimates of treatment efficacy. Exploratory analyses were performed to assess how our understanding of participant behaviors and their relationships to biological outcomes in two recent prevention trials might have been impacted had the frequency of routine behavioral data collection been reduced from monthly to just months 1, 3, 6, 9, and 12. Results were comparably informative in the reduced case, suggesting that unnecessarily extensive amounts of routine behavioral data may be collected in these trials.