Factors influencing the emergence and spread of HIV drug resistance arising from rollout of antiretroviral pre-exposure prophylaxis (PrEP)

Psychological and Behavioural Within-participant Predictors of Adherence to Oral HIV Pre-Exposure Prophylaxis (PrEP)

Oral PrEP's effectiveness relies on adequate adherence during periods of substantial HIV risk. Since most PrEP users will miss doses, understanding predictors within participants can help to explain adherence. We used a cross-sectional, within-participant design with 67 gay, bisexual, and other men who have sex with men taking PrEP daily. Using a questionnaire, informed by the Information Motivation Behavioral Skills Model, participants were asked about an adherent and a non-adherent episode. PrEP non-adherence was associated with non-normality of the day (p < .001), being out of the home (p < .001), weekend days (p = .01), having company (p = .02), using substances (p = 0.02), not using reminders (p = .03), lower PrEP information (p = .04), lower behavioural skills (p < .001) and less positive affect (p = .002). PrEP adherence assessment could focus on situational variations, supporting the construction of alternative strategies to facilitate adherence in these situations.

Enzyme Responsive Delivery of Anti-Retroviral Peptide via Smart Hydrogel

In response to an urgent need for advanced formulations for the delivery of anti-retrovirals, a stimuli-sensitive hydrogel formulation that intravaginally delivers HIV-1 entry inhibitor upon being exposed to a specific protease was developed. The hydrogel formulation consists of PEG-azide and PEG-DBCO covalently linked to the entry inhibitor peptide, enfuvirtide, via substrate linker that is designed to undergo proteolysis by prostate specific antigen (PSA) present in seminal fluid and release innate enfuvirtide. Of the tested PSA substrate linkers (HSSKLQYY, GISSFYSSK, AYLMYY, and AYLMGRR), HSSKLQ was found to be an optimal candidate for PEG-based hydrogel with k_cat/K_M of 2.2 M^-1 s^-1. The PEG-based hydrogel displayed a pseudoplastic, thixotropic behavior with overall viscosity varying between 1516 and 2.2 Pa.s, within the biologically relevant shear rates of 0.01-100 s^-1. It also exhibited viscoelastic properties appropriate for uniform spreading and being retained in vagina. PEG-based hydrogels were loaded with N3-HSSKLQ-enfuvirtide (HF42) that is customarily synthesized enfuvirtide prodrug with its N-terminus connected to HSSKLQ linker. The stimuli-sensitive PEG-based hydrogel formulations upon being exposed to PSA released 36.5 ± 4.8% of enfuvirtide over 24 h in human ejaculate mimic of vaginal simulant fluid and seminal simulant fluid mixed in 1:3 ratio, which is significantly greater than its IC₅₀. The PEG-based hydrogel was non-cytotoxic to both vaginal epithelial cells (VK2/E6E7) and murine macrophages (RAW 264.7) and did not significantly induce the production of nitric oxide, an inflammatory mediator. The PEG-based hydrogel is found to have suitable physicochemical properties for an intravaginal formulation of the PSA substrate-linked anti-retrovirals and is safe towards vaginal epithelium. It is capable of delivering enfuvirtide with effective concentrations to prevent women from HIV-1 infection.

Perceptions and Practicalities Influencing Pre-exposure Prophylaxis Adherence Among Men Who Have Sex with Men in England

PrEP is highly effective for HIV prevention but requires adequate adherence. In this paper we use the perceptions and practicalities approach (PAPA) to identify factors that influenced PrEP adherence using qualitative data from the PROUD study. From February 2014 to January 2016, we interviewed 41 gay, bisexual and other men-who-have-sex-with-men and one trans woman who were enrolled in the study. We purposively recruited participants for interview based on trial arm allocation, adherence and sexual risk behaviours. The interviews were conducted in English, audio-recorded, transcribed, coded and analysed using framework analysis. Participants in general were highly motivated to use and adhere to PrEP, and this was linked to strong perceptions of personal necessity for PrEP as they felt at risk of HIV and viewed PrEP as highly effective. On the other hand, concerns about side effects and HIV resistance did inhibit PrEP initiation and adherence although this was uncommon. Practical factors such as daily routine, existing habitual pill-taking and pill storage impacted adherence. Drug and alcohol use rarely caused participants to miss doses. These findings indicate that using the principals of PAPA to unpick influencers of PrEP use, could help tailor adherence support in PrEP programmes.

Acute HIV at the Time of Initiation of Pre-exposure or Post-exposure Prophylaxis: Impact on Drug Resistance and Clinical Outcomes

BACKGROUND

Initiating pre-exposure or post-exposure prophylaxis (PrEP/PEP) in the setting of undiagnosed acute HIV (AHI) could cause antiretroviral resistance. We sought to characterize clinical outcomes and drug resistance mutations among individuals prescribed PrEP/PEP with undiagnosed AHI at a San Francisco sexually transmitted disease clinic.

SETTING

In our PrEP/PEP program, patients are tested for HIV using a point-of-care antibody test. If negative, patients are started on prophylaxis and screened for AHI using pooled HIV RNA (5-10 days turn-around). We used 2-drug PEP until 05/2016.

METHODS

We identified patients who had as-yet-undiagnosed AHI on the day of PrEP/PEP start between 2011 and 2018, then used our clinical record and surveillance data to describe HIV resistance and clinical outcomes.

RESULTS

Of 1758 PrEP and 2242 PEP starts, there were 7 AHI cases among PrEP users (0.40%) and 6 among PEP users (0.30%). Median times for linkage to HIV care, initiation of HIV treatment, and viral suppression were 7, 12, and 43 days. On initiation of HIV care, 3 patients (23%) were found to have an M184 mutation 7-12 days after starting PrEP/PEP. All 3 had genotyping performed on stored serum available from the date of PrEP/PEP start, each of which demonstrated wild-type virus. All 3 patients achieved durable viral suppression.

CONCLUSIONS

Although rare (occurring <0.5% of the time), AHI in the setting of PrEP/2-drug PEP can result in an M184 within days. Even with M184, persons with AHI achieve viral suppression when rapidly linked to care and initiated on antiretroviral therapy. Providers should consider AHI screening when starting PrEP/PEP.

Attitude of infectious diseases physicians in Turkey about HIV pre-exposure prophylaxis: results of an online survey

Pre-exposure prophylaxis (PrEP) is the provision of antiretroviral drugs before HIV exposure to prevent infection for those in whom it is indicated. We conducted an online survey about PrEP in a national sample of infectious diseases physicians in Turkey. They were surveyed from March to April 2019 and they were asked about their attitudes, knowledge and clinical practise about PrEP. Overall, 209 of 2100 (10%) completed the survey, of whom 66.3% were female, 69.5% were specialist and 41.1% were working at education and research hospitals. Most of the participants reported their PrEP knowledge as 'low'. Men who have sex with men was the most suitable group for PrEP according to participants. 27.9% of them were requested to prescribe PrEP which was to be paid by individuals themselves and 24.2% of the participants had recommended PrEP in their clinical practice. The primary concerns among those who would not recommend PrEP were the possible increase in sexually transmitted infections, the potential low cost-effectiveness of PrEP, the ineffectiveness of PrEP in HIV transmission and the time lost to following-up the individuals taking PrEP. Developing a national guideline would support clinicians in order to change their attitudes and to find answers to their concerns.

"I'm doing this test so I can benefit from PrEP": exploring HIV testing barriers/facilitators and implementation of pre-exposure prophylaxis among South African adolescents

In South Africa, adolescents are a key population in the HIV epidemic that can benefit from increased access to oral pre-exposure prophylaxis (PrEP). HIV testing is an integral component of the PrEP care continuum but adolescents in South Africa have generally low HIV testing rates; therefore, adolescents' HIV testing attitudes and behaviours must be understood to develop strategies for effective PrEP implementation. Ten focus groups were conducted with adolescents living with HIV and HIV-uninfected adolescents (n = 55), and in-depth interviews were conducted with service providers (n = 25), adolescents living with HIV (n = 10) and HIV-uninfected adolescents (n = 25). Data were collected in the Western Cape province of South Africa from 2015-2016. Thematic framework analysis was used to understand dynamics by which South African adolescents' attitudes toward HIV testing might influence intended uptake of PrEP and, reciprocally, to explore the implications of adolescents' perceptions about PrEP availability for their willingness to engage in HIV testing. While South African adolescents' current HIV testing attitudes and behaviours present barriers to intended PrEP implementation in this population, increased access to PrEP has the potential to improve their initial HIV testing rates and decrease stigma and fear around HIV testing. However, implementation of PrEP must consider specific HIV testing barriers for adolescent boys and girls, respectively. As PrEP becomes more widely available for adolescents, possible challenges noted by participants may include the potential for adolescents to reduce continued HIV testing behaviours while on PrEP and to share/use unprescribed PrEP medications among peers.

A case of M184V mutant human immunodeficiency virus in a patient using daily pre-exposure prophylaxis

This study presents a case report of a 31-year-old gay man who acquired human immunodeficiency virus while using daily emtricitabine (FTC)/tenofovir disoproxil fumarate (TDF) pre-exposure prophylaxis (PrEP). He had an M184V nucleoside reverse-transcriptase inhibitor mutation at diagnosis. Either he acquired a pre-existing M184V mutation or he acquired a wild-type virus but then suboptimal use of FTC/TDF led to the development of resistance. For PrEP to be safely managed and seroconvertors to be identified quickly, PrEP should be commissioned by the NHS and managed within sexual health clinics. Notwithstanding the current provision of PrEP, those accessing it must be reminded about the importance of regular testing and optimal adherence.

Drug Resistance During HIV Pre-Exposure Prophylaxis

Clinical studies have demonstrated that use of tenofovir disoproxil fumarate with or without emtricitabine as antiretroviral pre-exposure prophylaxis (PrEP) can decrease the risk of human immunodeficiency virus (HIV) acquisition when medication adherence is high. However, the potential for PrEP to promote antiretroviral resistance remains an important public health consideration. We performed a search of the medical literature to identify studies that address HIV drug resistance during PrEP use. In this review, we summarize findings about emergent drug resistance during clinical trials of PrEP, case reports of seroconversions in patients adherent to PrEP, and animal studies of PrEP effectiveness against drug-resistant viral strains. We also discuss the potential utility of novel PrEP formulations for protection against drug-resistant HIV, the impact of drug resistance on HIV treatment options, and mathematical models that estimate the potential contribution of PrEP to population-level drug resistance. Evidence suggests that selection for HIV drug resistance with PrEP use is infrequent and most likely to occur when PrEP is used during undiagnosed acute HIV infection. Breakthrough infections during PrEP use with high adherence are possible, but appear to be rare. The prevalence of drug-resistant HIV strains needs to be monitored as PrEP is scaled up. However, the benefit of a decreased HIV incidence with wider PrEP use is likely to outweigh the risk of harms from possible increases in the prevalence of HIV drug resistance.

The impact, cost and cost-effectiveness of oral pre-exposure prophylaxis in sub-Saharan Africa: a scoping review of modelling contributions and way forward

INTRODUCTION

Oral pre-exposure prophylaxis (PrEP) is a new form of HIV prevention being considered for inclusion in national prevention portfolios. Many mathematical modelling studies have been undertaken that speak to the impact, cost and cost-effectiveness of PrEP programmes. We assess the available evidence from mathematical modelling studies to inform programme planning and policy decision making for PrEP and further research directions.

METHODS

We conducted a scoping review of the published modelling literature. Articles published in English which modelled oral PrEP in sub-Saharan Africa, or non-specific settings with relevance to generalized HIV epidemic settings, were included. Data were extracted for the strategies of PrEP use modelled, and the impact, cost and cost-effectiveness of PrEP for each strategy. We define an algorithm to assess the quality and relevance of studies included, summarize the available evidence and identify the current gaps in modelling. Recommendations are generated for future modelling applications and data collection.

RESULTS AND DISCUSSION

We reviewed 1924 abstracts and included 44 studies spanning 2007 to 2017. Modelling has reported that PrEP can be a cost-effective addition to HIV prevention portfolios for some use cases, but also that it would not be cost-effective to fund PrEP before other prevention interventions are expanded. However, our assessment of the quality of the modelling indicates cost-effectiveness analyses failed to comply with standards of reporting for economic evaluations and the assessment of relevance highlighted that both key parameters and scenarios are now outdated. Current evidence gaps include modelling to inform service development using updated programmatic information and ex post modelling to evaluate and inform efficient deployment of resources in support of PrEP, especially among key populations, using direct evidence of cost, adherence and uptake patterns.

CONCLUSIONS

Updated modelling which more appropriately captures PrEP programme delivery, uses current intervention scenarios, and is parameterized with data from demonstration and implementation projects is needed in support of more conclusive findings and actionable recommendations for programmes and policy. Future analyses should address these issues, aligning with countries to support the needs of programme planners and decision makers for models to more directly inform programme planning and policy.

Population-level mathematical modeling of antimicrobial resistance: a systematic review

BACKGROUND

Mathematical transmission models are increasingly used to guide public health interventions for infectious diseases, particularly in the context of emerging pathogens; however, the contribution of modeling to the growing issue of antimicrobial resistance (AMR) remains unclear. Here, we systematically evaluate publications on population-level transmission models of AMR over a recent period (2006-2016) to gauge the state of research and identify gaps warranting further work.

METHODS

We performed a systematic literature search of relevant databases to identify transmission studies of AMR in viral, bacterial, and parasitic disease systems. We analyzed the temporal, geographic, and subject matter trends, described the predominant medical and behavioral interventions studied, and identified central findings relating to key pathogens.

RESULTS

We identified 273 modeling studies; the majority of which (> 70%) focused on 5 infectious diseases (human immunodeficiency virus (HIV), influenza virus, Plasmodium falciparum (malaria), Mycobacterium tuberculosis (TB), and methicillin-resistant Staphylococcus aureus (MRSA)). AMR studies of influenza and nosocomial pathogens were mainly set in industrialized nations, while HIV, TB, and malaria studies were heavily skewed towards developing countries. The majority of articles focused on AMR exclusively in humans (89%), either in community (58%) or healthcare (27%) settings. Model systems were largely compartmental (76%) and deterministic (66%). Only 43% of models were calibrated against epidemiological data, and few were validated against out-of-sample datasets (14%). The interventions considered were primarily the impact of different drug regimens, hygiene and infection control measures, screening, and diagnostics, while few studies addressed de novo resistance, vaccination strategies, economic, or behavioral changes to reduce antibiotic use in humans and animals.

CONCLUSIONS

The AMR modeling literature concentrates on disease systems where resistance has been long-established, while few studies pro-actively address recent rise in resistance in new pathogens or explore upstream strategies to reduce overall antibiotic consumption. Notable gaps include research on emerging resistance in Enterobacteriaceae and Neisseria gonorrhoeae; AMR transmission at the animal-human interface, particularly in agricultural and veterinary settings; transmission between hospitals and the community; the role of environmental factors in AMR transmission; and the potential of vaccines to combat AMR.

Risk Perception, Sexual Behaviors, and PrEP Adherence Among Substance-Using Men Who Have Sex with Men: a Qualitative Study

The antiretroviral drug combination emtricitabine and tenofovir disoproxil fumarate (TDF/FTC) taken as pre-exposure prophylaxis (PrEP) is effective in preventing HIV infection, yet it also requires adherence and potentially decreases condom use. This study sought to examine these issues among a key population at risk of HIV infection, substance-using men who have sex with men (MSM). We conducted semi-structured interviews with an ethnically diverse sample of 30 young (aged 20-35) MSM prescribed PrEP within a large integrated healthcare system in San Francisco, who had reported recent drug use or hazardous drinking and one or more missed doses of PrEP. We explored participants' risk perception and sexual risk behavior, drug and alcohol use, and PrEP adherence in the context of substance use. Interviews were transcribed and coded using a directed content analysis approach to identify key categories and commonalities, and differences across participants. Salient subcategories included positive psychological effects of being on PrEP (e.g., decreased anxiety, feelings of empowerment), social effects (e.g., reduced HIV stigma), and reduction in overall perceptions of HIV risk. While overall reported use of condoms went down and many reported a brief period of increased condomless sex following PrEP initiation, others continued condom use with most of their sexual partners. Contextual factors influencing their decision to engage in condomless sex included how well they knew the partner and whether the partner was on PrEP or HIV antiretroviral treatment. Factors associated with poor adherence included disruptions in daily routine and use of alcohol and methamphetamine. PrEP-prescribing clinicians should support their patients in making informed decisions about condom use and identifying strategies to maximize adherence in the context of substance use.

Pre-exposure prophylaxis (PrEP) in an era of stalled HIV prevention: Can it change the game?

Pre-exposure prophylaxis (PrEP) for HIV prevention has evolved significantly over the years where clinical trials have now demonstrated the efficacy of oral PrEP, and the field is scaling-up implementation. The WHO and UNAIDS have made PrEP implementation a priority for populations at highest risk, and several countries have developed guidelines and national plans accordingly, largely based on evidence generated by demonstration projects. PrEP presents the opportunity to change the face of HIV prevention by offering a new option for protection against HIV and disrupting current HIV prevention systems. Nevertheless, as with all new technologies, both practical and social requirements for implementation must be taken into account if there is to be sustained and widespread adoption, which will also apply to forthcoming prevention technologies. Defining and building success for PrEP within the scope of scale-up requires careful consideration. This review summarises where the PrEP field is today, lessons learned from the past, the philosophy and practicalities of how successful programming may be defined, and provides perspectives of costs and affordability. We argue that a successful PrEP programme is about effective intervention integration and ultimately keeping people HIV negative.

PrEP Adherence Patterns Strongly Affect Individual HIV Risk and Observed Efficacy in Randomized Clinical Trials

BACKGROUND

Randomized controlled trials (RCTs) suggest that the efficacy of tenofovir-based preexposure prophylaxis (PrEP) strongly depends on the consistency of PrEP use. We explore how the patterns of pill taking and waning of PrEP protection may affect PrEP efficacy for HIV prevention.

METHODS

A 2-arm RCT was simulated by mathematical models assuming that the prescribed daily doses were skipped periodically, randomly, or in large blocks. Risk-driven adherence, in which PrEP was taken when sex was expected, was also investigated. Three temporal PrEP protection profiles were explored: long (5 days), intermediate (3 days), and short (24 hours). Modeling results were compared to the efficacy observed in completed RCTs.

RESULTS

The expected PrEP efficacy was 60% with periodic, 50% with random, and 34% with block adherence when PrEP had a long protection profile and pills were taken only 50% of the days. Risk-driven pill taking resulted in 29% and 37% daily pills taken and efficacy of 43% and 51%, respectively, for long protection. High PrEP efficacy comparable with that observed in Partners PrEP and Centers for Disease Control and Prevention Botswana trials was simulated under long protection, high overall adherence, and limited block pill taking; the moderate efficacy observed in iPrEx and Bangkok trials was comparable with the 50% adherence scenarios under random pill taking and long protection.

CONCLUSIONS

Pill-taking patterns may have a substantial impact on the protection provided by PrEP even when the same numbers of pills are taken. When PrEP retains protection for longer than a day, pill-taking patterns can explain a broad range of efficacies observed in PrEP RCTs.

Future technologies for monitoring HIV drug resistance and cure

PURPOSE OF REVIEW

Sensitive, scalable and affordable assays are critically needed for monitoring the success of interventions for preventing, treating and attempting to cure HIV infection. This review evaluates current and emerging technologies that are applicable for both surveillance of HIV drug resistance (HIVDR) and characterization of HIV reservoirs that persist despite antiretroviral therapy and are obstacles to curing HIV infection.

RECENT FINDINGS

Next-generation sequencing (NGS) has the potential to be adapted into high-throughput, cost-efficient approaches for HIVDR surveillance and monitoring during continued scale-up of antiretroviral therapy and rollout of preexposure prophylaxis. Similarly, improvements in PCR and NGS are resulting in higher throughput single genome sequencing to detect intact proviruses and to characterize HIV integration sites and clonal expansions of infected cells.

SUMMARY

Current population genotyping methods for resistance monitoring are high cost and low throughput. NGS, combined with simpler sample collection and storage matrices (e.g. dried blood spots), has considerable potential to broaden global surveillance and patient monitoring for HIVDR. Recent adaptions of NGS to identify integration sites of HIV in the human genome and to characterize the integrated HIV proviruses are likely to facilitate investigations of the impact of experimental 'curative' interventions on HIV reservoirs.

Reporting on the prevalence of antiretroviral drug resistance in a regional HIV population over 20 years: a word of caution

BACKGROUND

Failure to achieve complete viral suppression with antiretroviral drugs (ARV) may lead to uncontrolled HIV replication, ARV resistance and negative outcomes. Monitoring and reporting of HIV resistance trends is important but problematic. We examined prevalent resistance rates in an HIV population over 20 years and document how rates may appear to vary greatly based solely on which parameters are utilized.

METHODS

We determined the annual use of genotypic antiretroviral resistance testing (GART) from 1995 to 2014 for all patients receiving HIV care in southern Alberta, Canada, and the presence of resistance mutations in those tested. The impact on prevalent resistance rates of using cumulative or latest GART was also determined.

RESULTS

Between 1995 and 2014, the number of patients with GART increased from <1% to 71%. Prevalent resistance in patients with GART decreased from a high of 52% in 2003 to 25.8% in 2014. However, if prevalence rates were reported using all active patients as denominator, including those without GART, prevalence increased from 0.7% to 18.5%. Prevalence rates were 7% to 9% higher in any given year if cumulative GART rather than latest GART results were used.

CONCLUSIONS

While prevalence resistance rates are decreasing, the precise rates being reported may vary due to increasing number of patients tested annually, using either the entire population as denominator or only patients with GART, and using either last or cumulative GART. Defining these parameters is critical if prevalence is to be compared over time or between HIV populations.

Oral preexposure prophylaxis to prevent HIV infection: clinical and public health implications

This article reviews the use of combination emtricitabine (FTC)/tenofovir as preexposure prophylaxis (PrEP) for HIV-negative patients at high risk of acquiring HIV, including heterosexual men and women, men who have sex with men, and IV drug users. When used with classic prevention strategies such as condoms, PrEP has been found effective in reducing the risk of HIV transmission.

Should we fear resistance from tenofovir/emtricitabine preexposure prophylaxis?

PURPOSE OF REVIEW

To review current data on HIV-1 resistance arising from the use of fixed dose combination tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) for preexposure prophylaxis (PrEP) to prevent HIV-1 infection.

RECENT FINDINGS

Resistance to tenofovir (TNV) or FTC is infrequently selected by TDF/FTC PrEP if started before HIV-1 infection has occurred, but is much more common when inadvertently started during undiagnosed acute infection. Mathematical modeling predicts that the number of HIV-1 infections averted by the use of PrEP far exceeds the increase in drug-resistant infections that could occur from PrEP. Studies in macaques show that TNV-resistant virus but not FTC-resistant virus can cause breakthrough infection despite TDF/FTC PrEP. FTC resistance with M184 V/I occurs more frequently than TFV resistance with K65R in seroconverters from clinical trials of TDF/FTC PrEP.

SUMMARY

The benefit of preventing HIV-1 infections with TDF/FTC PrEP far outweighs the risk of drug-resistant infection, provided PrEP is not started in persons with undiagnosed HIV-1 infection. We should respect but not fear HIV-1 resistance from TDF/FTC PrEP and recognize that most TNV or FTC resistance will arise from its use for antiretroviral therapy (ART). Preventing ART failure or detecting it early is most important for preventing the spread of HIV-1 resistance to TDF/FTC and preserving its effectiveness for both PrEP and ART.

How Much Do We Know about Drug Resistance Due to PrEP Use? Analysis of Experts' Opinion and Its Influence on the Projected Public Health Impact

BACKGROUND

Randomized controlled trials reported that pre-exposure prophylaxis (PrEP) with tenofovir and emtricitabine rarely selects for drug resistance. However, drug resistance due to PrEP is not completely understood. In daily practice, PrEP will not be used under the well-controlled conditions available in the trials, suggesting that widespread use of PrEP can result in increased drug resistance.

METHODS

We surveyed expert virologists with questions about biological assumptions regarding drug resistance due to PrEP use. The influence of these assumptions on the prevalence of drug resistance and the fraction of HIV transmitted resistance was studied with a mathematical model. For comparability, 50% PrEP-coverage of and 90% per-act efficacy of PrEP in preventing HIV acquisition are assumed in all simulations.

RESULTS

Virologists disagreed on the following: the time until resistance emergence (range: 20-180 days) in infected PrEP users with breakthrough HIV infections; the efficacy of PrEP against drug-resistant HIV (25%-90%); and the likelihood of resistance acquisition upon transmission (10%-75%). These differences translate into projections of 0.6%- 1% and 3.5%-6% infected individuals with detectable resistance 10 years after introducing PrEP, assuming 100% and 50% adherence, respectively. The rate of resistance emergence following breakthrough HIV infection and the rate of resistance reversion after PrEP use is discontinued, were the factors identified as most influential on the expected resistance associated with PrEP. Importantly, 17-23% infected individuals could virologically fail treatment as a result of past PrEP use or transmitted resistance to PrEP with moderate adherence.

CONCLUSIONS

There is no broad consensus on quantification of key biological processes that underpin the emergence of PrEP-associated drug resistance. Despite this, the contribution of PrEP use to the prevalence of the detectable drug resistance is expected to be small. However, individuals who become infected despite the use of PrEP should be closely monitored due to higher risk of virological failure when initiating antiretroviral treatment in the future.

Views of HIV-negative partners in heterosexual serodiscordant relationships regarding HIV pre-exposure prophylaxis: a qualitative study

Background: Pre-exposure prophylaxis (PrEP) may be an effective option for HIV prevention among heterosexual serodiscordant couples. However, there are knowledge gaps in social research about PrEP in heterosexual serodiscordant relationships, including motivations and barriers to its use and possible impacts of PrEP uptake on the sexual practices of these couples. The aim of this study was to explore the views of HIV-negative men and women in stable serodiscordant heterosexual relationships about the possible use of PrEP. Methods: Semi-structured interviews were used to understand participants' views on the use of PrEP. Interviews were conducted face-to-face or by telephone and transcribed verbatim for thematic analysis. Results: In total, 13 HIV-negative partners were interviewed; six men and seven women. Participants demonstrated a high interest in the use of PrEP for conception. PrEP was also considered an option for general HIV prevention, although men saw more benefits for this use than women. Participants' main concerns around PrEP usage were about cost, efficacy, daily adherence and side-effects. HIV-positive partner support is likely to play a central role for PrEP uptake and adherence. Conclusions: This study is one of the first studies to explore the views of HIV-negative heterosexual partners in serodiscordant relationships around the use of PrEP while trying to conceive, as well as for general HIV prevention. These study results provide new insights for the further development of guidelines governing the use of PrEP for serodiscordant couples.

Frequency of HIV testing among gay and bisexual men in the UK: implications for HIV prevention

Objectives

The aim of the study was to explore HIV testing frequency among UK men who have sex with men (MSM) in order to direct intervention development.

Methods

Cross‐sectional surveys were completed by 2409 MSM in Edinburgh, Glasgow and London in 2011 and a Scotland‐wide online survey was carried out in 2012/13. The frequency of HIV testing in the last 2 years was measured.

Results

Overall, 21.2% of respondents reported at least four HIV tests and 33.7% reported two or three tests in the last 2 years, so we estimate that 54.9% test annually. Men reporting at least four HIV tests were younger and less likely to be surveyed in London. They were more likely to report higher numbers of sexual and anal intercourse partners, but not “higher risk” unprotected anal intercourse (UAI) with at least two partners, casual partners and/or unknown/discordant status partners in the previous 12 months. Only 26.7% (238 of 893) of men reporting higher risk UAI reported at least four tests. Among all testers (n = 2009), 56.7% tested as part of a regular sexual health check and 35.5% tested following a risk event. Differences were observed between surveys, and those testing in response to a risk event were more likely to report higher risk UAI.

Conclusions

Guidelines recommend that all MSM test annually and those at “higher risk” test more frequently, but our findings suggest neither recommendation is being met. Additional efforts are required to increase testing frequency and harness the opportunities provided by biomedical HIV prevention. Regional, demographic and behavioural differences and variations in the risk profiles of testers suggest that it is unlikely that a “one size fits all” approach to increasing the frequency of testing will be successful.

How could preventive therapy affect the prevalence of drug resistance? Causes and consequences

Various forms of preventive and prophylactic antimicrobial therapies have been proposed to combat HIV (e.g. pre-exposure prophylaxis), tuberculosis (e.g. isoniazid preventive therapy) and malaria (e.g. intermittent preventive treatment). However, the potential population-level effects of preventative therapy (PT) on the prevalence of drug resistance are not well understood. PT can directly affect the rate at which resistance is acquired among those receiving PT. It can also indirectly affect resistance by altering the rate at which resistance is acquired through treatment for active disease and by modifying the level of competition between transmission of drug-resistant and drug-sensitive pathogens. We propose a general mathematical model to explore the ways in which PT can affect the long-term prevalence of drug resistance. Depending on the relative contributions of these three mechanisms, we find that increasing the level of coverage of PT may result in increases, decreases or non-monotonic changes in the overall prevalence of drug resistance. These results demonstrate the complexity of the relationship between PT and drug resistance in the population. Care should be taken when predicting population-level changes in drug resistance from small pilot studies of PT or estimates based solely on its direct effects.

Role of oral pre-exposure prophylaxis (PrEP) in current and future HIV prevention strategies

Treatment as prevention is expected to have a major role in reducing HIV incidence, but other prevention interventions will also be required to bring the epidemic under control, particularly among key populations. One or more forms of pre-exposure prophylaxis (PrEP) will likely play a critical role. Oral PrEP with emtricitabine-tenofovir (Truvada®) is currently available in the US and some other countries, but uptake has been slow. We review the concerns that have contributed to this slow uptake and discuss current and future research in this critical area of HIV prevention research.

Healthcare providers' knowledge of, attitudes to and practice of pre-exposure prophylaxis for HIV infection

OBJECTIVES

Pre-exposure prophylaxis (PrEP) has proven biological efficacy in reducing the risk of sexual acquisition of HIV. Healthcare providers' (HCPs) knowledge of and attitudes to PrEP will be key to successful implementation. In England, PrEP is only available to men who have sex with men (MSM) through the open-label randomized PROUD pilot study of immediate or deferred use.

METHODS

In September 2013, a cross-sectional survey of UK HCPs distributed through sexual health clinics (219) and professional societies' email lists (2599) and at a conference (80) asked about knowledge of, attitudes to and practice of PrEP.

RESULTS

Overall, 328 of 2898 (11%) completed the survey, of whom 160 of 328 (49%) were doctors, 51 (16%) sexual health advisers (SHAs), 44 (14%) nurses and 73 (22%) unspecified. Over a quarter (83 of 311; 27%) were involved in PROUD. Most respondents (260 of 326; 80%) rated their knowledge of PrEP as medium or high. Over half of respondents (166 of 307; 54%) thought PrEP should be available outside of a clinical trial. The main barriers to supporting PrEP availability outside a clinical trial were concerns about current evidence (odds ratio [OR] 0.13), lack of UK-specific guidance (OR 0.35), concerns about adherence (OR 0.38) and risk of sexual or physical coercion for patients to have condomless or higher risk sex (OR 0.42 in multivariate regression). Just over half (147 of 277; 53%) had been asked about PrEP by patients in the past year, including almost half of those working in a clinic not involved in the PROUD study (86 of 202; 43%).

CONCLUSIONS

There is support for PrEP availability outside a clinical trial, but HCPs have residual concerns about its effectiveness and negative consequences, and the absence of UK-specific implementation guidance.

Targeting pre-exposure prophylaxis among men who have sex with men in the United States and Peru: partnership types, contact rates, and sexual role

BACKGROUND

We aim to identify optimal strategies for deploying pre-exposure prophylaxis among men who have sex with men (MSM) in the United States and Peru to maximize population-level effectiveness in an efficient manner. We use epidemic models to simulate the impact of targeting strategies. Most studies have focused on targeting either the general population or high-risk MSM. Alternative strategies, including serodiscordant couples, may better balance effectiveness and efficiency.

METHODS

We use dynamic stochastic sexual network models based on exponential-family random graph modeling, parameterized from behavioral surveys of MSM in the United States and Peru. These models represent main partnerships and casual contacts separately, permitting modeling of interventions targeting men whose risk derives from combinations of relational types. We also model varying rates of uptake and adherence to pre-exposure prophylaxis (PrEP). We assess sensitivity of results to risk compensation through increases in condomless casual contacts and condomless sex in main partnerships.

RESULTS

Targeting all men who are not exclusively insertive has the largest impact on HIV incidence, but targeting only those with high levels of casual activity yields comparable results using fewer person-years on PrEP. The effect is robust to risk compensation in the United States, but less so in Peru. Targeting serodiscordant main partnerships does not significantly impact incidence, but requires fewer person-years on PrEP per infection averted than other strategies.

CONCLUSIONS

PrEP could be effective in reducing new infections at the population level in both settings. Serodiscordant partnerships are an attractive component of a targeting program, but targeting should include other high-risk men.

"Why should I take drugs for your infection?": outcomes of formative research on the use of HIV pre-exposure prophylaxis in Nigeria

BACKGROUND

Nigeria has the second highest number of new HIV infections annually. Therefore, it is important to explore new strategies for preventing new infections. The introduction of pre-exposure prophylaxis (PrEP) for use by persons at high risk of HIV infection has new potential in preventing new HIV infections. The aim of this study is to explore the public opinion, community interest, and perceptions about the use and access to PrEP in Nigeria.

METHODS

This formative study used a mixed method approach to collect data on public opinions and perceptions on appropriate target groups for PrEP access, community interest, perceptions about the use of PrEP as an HIV-prevention tool, how best to communicate with participants about PrEP, concerns about PrEP use by serodiscordant couples, and suggestions for the design and implementation of a PrEP demonstration project. Telephone and in-depth interviews were conducted, and focus group discussions and consultative meetings were held with critical stakeholders engaged in HIV-prevention, treatment, care, and support programmes in Nigeria. An online survey was also conducted.

RESULTS

HIV serodiscordant couples were identified as the appropriate target group for PrEP use. Most respondents felt that PrEP use by key affected populations would help reduce the HIV incidence. Stigma was identified as a major concern and a potential barrier for the acceptance and use of PrEP by HIV serodiscordant couples. Electronic and print media were identified as important means for massive public education to prevent stigma and create awareness about PrEP. In a male dominated society such as Nigeria, HIV-negative male partners in serodiscordant relationships may resist enrolment in PrEP programmes. This may be complicated by the fact that the identified index partner in most serodiscordant relationships in Nigeria is an HIV-positive woman, who is often diagnosed during pregnancy.

CONCLUSIONS

PrEP uptake and use by HIV serodiscordant couples in Nigeria may face notable but surmountable challenges. Much depends on the appropriateness of actions taken by multiple players. Motivation of HIV-negative male partners to use PrEP and establishment of effective public education programmes in addressing stigma are essential.

HIV treatment as prevention: contradictory perspectives from dynamic mathematical models

The preventative effects of antiretroviral therapy for people with HIV have been debated since they were first raised. Models commenced studying the preventive effects of treatment in the 1990s, prior to initial public reports. However, the outcomes of the preventive effects of antiretroviral use were not consistent. Some outcomes of dynamic models were based on unfeasible assumptions, such as no consideration of drug resistance, behavior disinhibition, or economic inputs in poor countries, and unrealistic input variables, for example, overstated initiation time, adherence, coverage, and efficacy of treatment. This paper reviewed dynamic mathematical models to ascertain the complex effects of ART on HIV transmission. This review discusses more conservative inputs and outcomes relative to antiretroviral use in HIV infections in dynamic mathematical models. ART alone cannot eliminate HIV transmission.

Oral pre-exposure prophylaxis (PrEP) for prevention of HIV in serodiscordant heterosexual couples in the United States: opportunities and challenges

Oral HIV pre-exposure prophylaxis (PrEP) is a promising new biomedical prevention approach in which HIV-negative individuals are provided with daily oral antiretroviral medication for the primary prevention of HIV-1. Several clinical trials have demonstrated efficacy of oral PrEP for HIV prevention among groups at high risk for HIV, with adherence closely associated with level of risk reduction. In the United States (US), three groups have been prioritized for initial implementation of PrEP-injection drug users, men who have sex with men at substantial risk for HIV, and HIV-negative partners within serodiscordant heterosexual couples. Numerous demonstration projects involving PrEP implementation among MSM are underway, but relatively little research has been devoted to study PrEP implementation in HIV-serodiscordant heterosexual couples in the US. Such couples face a unique set of challenges to PrEP implementation at the individual, couple, and provider level with regard to PrEP uptake and maintenance, adherence, safety and toxicity, clinical monitoring, and sexual risk behavior. Oral PrEP also provides new opportunities for serodiscordant couples and healthcare providers for primary prevention and reproductive health. This article provides a review of the critical issues, challenges, and opportunities involved in the implementation of oral PrEP among HIV-serodiscordant heterosexual couples in the US.

Practical guidance for nonoccupational postexposure prophylaxis to prevent HIV infection: an editorial review

Postexposure prophylaxis (PEP) with antiretroviral medication has been used as an HIV-prevention strategy for nearly 20 years. The fact that approximately 50 000 new HIV infections occur in the United States each year reflects marked underutilization of nonoccupational PEP (NPEP). There have been several advances in NPEP in the past 10 years. Clinical trials from different countries have demonstrated better tolerability, completion rates, and fewer drug-drug interactions with newer antiretroviral agents. Notably, there has been a shift from zidovudine-based to tenofovir-based regimens. Three-drug therapy is now favored for all potential HIV exposures. More recently, the US Public Health Service and the New York State Department of Health recommended tenofovir/emtricitabine and raltegravir as the first-line regimen universally for PEP. Advances in HIV testing technology may also allow shorter duration of follow-up HIV testing after a high-risk exposure. This review will discuss challenges with previously recommended regimens, newer potential candidate agents and the rationale for using them, intervals for laboratory monitoring, and cost considerations for NPEP. NPEP can be viewed as an educable moment and a potential bridge to preexposure prophylaxis, as part of a combination prevention package, for those who are likely to have recurrent higher-risk exposures. Thus, risk-reduction counseling should be an integral aspect of NPEP.

Tenofovir-based HIV pre-exposure prophylaxis

HIV pre-exposure prophylaxis (PrEP) with daily oral tenofovir disoproxil fumarate (TDF) or TDF–emtricitabine (FTC) has been shown to be effective against sexual and injection-drug related HIV acquisition in four out of six large clinical trials. This article reviews the pharmacology of TDF and FTC as it relates both to PrEP efficacy and the emergence of viral resistance, summarizes the six trials and the inherent challenges to PrEP they highlighted, and proposes some future areas for further exploration.

Preexposure prophylaxis will have a limited impact on HIV-1 drug resistance in sub-Saharan Africa: a comparison of mathematical models

BACKGROUND

Preexposure prophylaxis (PrEP) with tenofovir and emtricitabine can prevent new HIV-1 infections, but there is a concern that use of PrEP could increase HIV drug resistance resulting in loss of treatment options. We compared standardized outcomes from three independent mathematical models simulating the impact of PrEP on HIV transmission and drug resistance in sub-Saharan African countries.

METHODS

All models assume that people using PrEP receive an HIV test every 3-6 months. The models vary in structure and parameter choices for PrEP coverage, effectiveness of PrEP (at different adherence levels) and the rate with which HIV drug resistance emerges and is transmitted.

RESULTS

The models predict that the use of PrEP in conjunction with antiretroviral therapy will result in a lower prevalence of HIV than when only antiretroviral therapy is used. With or without PrEP, all models suggest that HIV drug resistance will increase over the next 20 years due to antiretroviral therapy. PrEP will increase the absolute prevalence of drug resistance in the total population by less than 0.5% and amongst infected individuals by at most 7%. Twenty years after the introduction of PrEP, the majority of drug-resistant infections is due to antiretroviral therapy (50-63% across models), whereas 40-50% will be due to transmission of drug resistance, and less than 4% to the use of PrEP.

CONCLUSION

HIV drug resistance resulting from antiretroviral therapy is predicted to far exceed that resulting from PrEP. Concern over drug resistance should not be a reason to limit the use of PrEP.

Analytic review of modeling studies of ARV Based PrEP interventions reveals strong influence of drug-resistance assumptions on the population-level effectiveness

Background

Four clinical trials have shown that oral and topical pre-exposure prophylaxis (PrEP) based on tenofovir may be effective in preventing HIV transmission. The expected reduction in HIV transmission and the projected prevalence of drug resistance due to PrEP use vary significantly across modeling studies as a result of the broad spectrum of assumptions employed. Our goal is to quantify the influence of drug resistance assumptions on the predicted population-level impact of PrEP.

Methods

All modeling studies which evaluate the impact of oral or topical PrEP are reviewed and key assumptions regarding mechanisms of generation and spread of drug-resistant HIV are identified. A dynamic model of the HIV epidemic is developed to assess and compare the impact of oral PrEP using resistance assumptions extracted from published studies. The benefits and risks associated with ten years of PrEP use are evaluated under identical epidemic, behavioral and intervention conditions in terms of cumulative fractions of new HIV infections prevented, resistance prevalence among those infected with HIV, and fractions of infections in which resistance is transmitted.

Results

Published models demonstrate enormous variability in resistance-generating assumptions and uncertainty in parameter values. Depending on which resistance parameterization is used, a resistance prevalence between 2% and 44% may be expected if 50% efficacious oral PrEP is used consistently by 50% of the population over ten years. We estimated that resistance may be responsible for up to a 10% reduction or up to a 30% contribution to the fraction of prevented infections predicted in different studies.

Conclusions

Resistance assumptions used in published studies have a strong influence on the projected impact of PrEP. Modelers and virologists should collaborate toward clarifying the set of resistance assumptions biologically relevant to the PrEP products which are already in use or soon to be added to the arsenal against HIV.

Prevalence of HIV-1 drug resistance among women screening for HIV prevention trials in KwaZulu-Natal, South Africa (MTN-009)

BACKGROUND

A major concern with using antiretroviral (ARV)-based products for HIV prevention is the potential spread of drug resistance, particularly from individuals who are HIV-infected but unaware of their status. Limited data exist on the prevalence of HIV infection or drug resistance among potential users of ARV-based prevention products.

METHODS

A cross-sectional study of reproductive-aged women who presented to screen for an HIV prevention trial was conducted at 7 clinical sites in Durban, South Africa. CD4+T cell counts, HIV-1 RNA levels and population sequencing of the protease and reverse transcriptase genes were performed for all women with 2 positive HIV rapid tests. Resistance mutations were identified using the Stanford Calibrated Population Resistance Tool.

RESULTS

Of the 1073 evaluable women, 400(37%) were confirmed as HIV-infected. Of those, plasma HIV-1 RNA was detectable in 365/400(91%) and undetectable(<40 copies/ml) in 35/400(9%) women. 156 women(39%) were eligible for antiretroviral therapy (CD4+T cell counts<350 cells/mm(3)) and 50(13%) met criteria for AIDS(CD4<200 cells/mm(3)). Of 352 plasma samples(>200 copies/ml) analyzed for drug resistance, 26(7.4%) had nucleoside reverse transcriptase inhibitor (NRTI), non-nucleoside reverse transcriptase inhibitor (NNRTI) or protease inhibitor (PI) drug resistance mutations. Among those with resistance, 18/26 participants(62%) had single-class NNRTI resistance and 5/26(19%) had dual-class NRTI/NNRTI. Major mutations in reverse transcriptase included K65R(n = 1), L74I(n = 1), K103N(n = 19), V106M(n = 4), Y181C(n = 2), M184V(n = 4), and K219E/R(n = 2). Major PI-resistance mutations were rare: M46L(n = 1) and I85V(n = 1). All participants were infected with subtype C virus, except one infected with subtype A.

CONCLUSIONS

In women from Durban, South Africa screening for an HIV prevention trial, the HIV prevalence was high (37%) and HIV drug resistance prevalence was above 5%. This study highlights the potential challenges faced when implementing an ARV-based prevention product that overlaps with first-line antiretroviral therapy. Effective screening to exclude HIV infection among women interested in uptake of ARV-based HIV prevention will be essential in limiting the spread of ARV resistance.

Cost-effectiveness of pre-exposure prophylaxis (PrEP) in preventing HIV-1 infections in rural Zambia: a modeling study

BACKGROUND

Pre-exposure prophylaxis (PrEP) with tenofovir and emtricitabine effectively prevents new HIV infections. The optimal scenario for implementing PrEP where most infections are averted at the lowest cost is unknown. We determined the impact of different PrEP strategies on averting new infections, prevalence, drug resistance and cost-effectiveness in Macha, a rural setting in Zambia.

METHODS

A deterministic mathematical model of HIV transmission was constructed using data from the Macha epidemic (antenatal prevalence 7.7%). Antiretroviral therapy is started at CD4<350 cells/mm(3). We compared the number of infections averted, cost-effectiveness, and potential emergence of drug resistance of two ends of the prioritization spectrum: prioritizing PrEP to half of the most sexually active individuals (5-15% of the total population), versus randomly putting 40-60% of the total population on PrEP.

RESULTS

Prioritizing PrEP to individuals with the highest sexual activity resulted in more infections averted than a non-prioritized strategy over ten years (31% and 23% reduction in new infections respectively), and also a lower HIV prevalence after ten years (5.7%, 6.4% respectively). The strategy was very cost-effective at $323 per quality adjusted life year gained and appeared to be both less costly and more effective than the non-prioritized strategy. The prevalence of drug resistance due to PrEP was as high as 11.6% when all assumed breakthrough infections resulted in resistance, and as low as 1.3% when 10% of breakthrough infections resulted in resistance in both our prioritized and non-prioritized scenarios.

CONCLUSIONS

Even in settings with low test rates and treatment retention, the use of PrEP can still be a useful strategy in averting infections. Our model has shown that PrEP is a cost-effective strategy for reducing HIV incidence, even when adherence is suboptimal and prioritization is imperfect.

Considerations regarding antiretroviral chemoprophylaxis and heterosexuals in generalized epidemic settings

PURPOSE OF REVIEW

To discuss the factors pertinent to the use of pre-exposure prophylaxis (PrEP) by at-risk heterosexuals in countries with generalized HIV epidemics.

RECENT FINDINGS

PrEP will have the greatest prevention effect if targeted to those at highest risk, but identifying and engaging such persons is challenging. Serodiscordant couples account for a high proportion of new infections and are an appropriate target for PrEP, but the proportion of people in such relationships is small and outside partnerships are common. Differences in adherence coupled to pharmacology of the drugs may account for differences in efficacy seen in the trials. Mathematical modeling indicates that the benefits of PrEP in highly endemic settings outweigh the risk of induced viral resistance. Behavioral risk compensation was not observed in the trials, but current open-label studies will better determine if disinhibition will be an important problem.

CONCLUSIONS

PrEP is a potentially useful HIV-prevention strategy for generalized heterosexual epidemics. Optimal implementation will require learning more about ways to improve acceptability and adherence and how best to deliver PrEP within the context of limited resource availability.

A pill for HIV prevention: déjà vu all over again?

Recent FDA approval of tenofovir-emtricitabine for prevention of human immunodeficiency virus (HIV) as a form of pre-exposure prophylaxis (PrEP) has led to concern about implementation of this strategy. Fifty years ago, a very similar national and international debate occurred when the oral contraceptive pill ("the Pill" or "OCP") was approved. Contentious issues included OCP safety, cost, and the potential impact on sexual behavior--many of the same concerns being voiced currently about PrEP. In this article, we review the social and medical history of OCP, drawing parallels with the current PrEP debate. We also explore the key areas where PrEP differs from its forbear: lower efficacy, presence of drug resistance, and a more circumscribed (and marginalized) target population. A thoughtful approach to PrEP implementation, bearing in mind the historical insights gained from the 1960s, might serve as well as we begin this new chapter in the control of the HIV epidemic.

A model of HIV drug resistance driven by heterogeneities in host immunity and adherence patterns

Background

Population transmission models of antiretroviral therapy (ART) and pre-exposure prophylaxis (PrEP) use simplistic assumptions – typically constant, homogeneous rates – to represent the short-term risk and long-term effects of drug resistance. In contrast, within-host models of drug resistance allow for more detailed dynamics of host immunity, latent reservoirs of virus, and drug PK/PD. Bridging these two levels of modeling detail requires an understanding of the “levers” – model parameters or combinations thereof – that change only one independent observable at a time. Using the example of accidental tenofovir-based pre-exposure prophyaxis (PrEP) use during HIV infection, we will explore methods of implementing host heterogeneities and their long-term effects on drug resistance.

Results

We combined and extended existing models of virus dynamics by incorporating pharmacokinetics, pharmacodynamics, and adherence behavior. We identified two “levers” associated with the host immune pressure against the virus, which can be used to independently modify the setpoint viral load and the shape of the acute phase viral load peak. We propose parameter relationships that can explain differences in acute and setpoint viral load among hosts, and demonstrate their influence on the rates of emergence and reversion of drug resistance. The importance of these dynamics is illustrated by modeling long-lived latent reservoirs of virus, through which past intervals of drug resistance can lead to failure of suppressive drug regimens. Finally, we analyze assumptions about temporal patterns of drug adherence and their impact on resistance dynamics, finding that with the same overall level of adherence, the dwell times in drug-adherent versus not-adherent states can alter the levels of drug-resistant virus incorporated into latent reservoirs.

Conclusions

We have shown how a diverse range of observable viral load trajectories can be produced from a basic model of virus dynamics using immunity-related “levers”. Immune pressure, in turn, influences the dynamics of drug resistance, with increased immune activity delaying drug resistance and driving more rapid return to dominance of drug-susceptible virus after drug cessation. Both immune pressure and patterns of drug adherence influence the long-term risk of drug resistance. In the case of accidental PrEP use during infection, rapid transitions between adherence states and/or weak immunity fortifies the “memory” of previous PrEP exposure, increasing the risk of future drug resistance. This model framework provides a means for analyzing individual-level risks of drug resistance and implementing heterogeneities among hosts, thereby achieving a crucial prerequisite for improving population-level models of drug resistance.

Impact of Pill Sharing on Drug Resistance Due to a Wide-Scale Oral Prep Intervention in Generalized Epidemics

BACKGROUND

The first antiretroviral drug (Truvada) to be used as a pre-exposure prophylaxis (PrEP) in preventing HIV transmission is about to be approved. Behavioral studies suggest that a portion of users may share anti-retroviral drugs with sex partners, family, or friends. Pill sharing will decrease PrEP efficacy and adherence level, and potentially create an environment favorable for the development of drug resistance. We aim to evaluate the potential impact of pill sharing on the PrEP effectiveness and on the rates of drug-resistance development in heterosexual populations.

METHODS

A transmission dynamic model was used to assess the population-level impact of oral PrEP. The fractions of new HIV infections prevented (CPF), drug resistance prevalence and the proportion of new infections in which drug-resistant HIV is transmitted (TDR) are evaluated over fixed time periods. The influence of different factors on CPF and TDR is studied through simulations, using epidemic parameters representative of the countries in Sub-Saharan Africa.

RESULTS

Without pill sharing, a 70% efficacious PrEP used consistently by 60% of uninfected individuals prevents 52.8% (95% CI 49.4%-56.4%) of all new HIV infections over ten years with drug-resistant HIV transmitted in 2.2% of the new infections. Absolute CPF may vary by 9% if up to 20% of the users share PrEP while the level of TDR and total resistance prevalence may increase by up to 6-fold due to pill sharing in some intervention scenarios.

CONCLUSION

Pill sharing may increase the PrEP coverage level achieved in the population but it also affects the PrEP efficacy for the users who do not follow the prescribed schedule. More importantly, it creates a pool of untracked users who remain unreached by the effort to avoid sub-optimal PrEP usage by infected people. This increases substantially the potential risk of drug resistance in the population.

The Promise of Antiretrovirals for HIV Prevention

With an estimated 2.6 million new HIV infections diagnosed annually, the world needs new prevention strategies to partner with condom use, harm reduction approaches for injection drug users, and male circumcision. Antiretrovirals can reduce the risk of mother-to-child HIV transmission and limit HIV acquisition after occupational exposure. Macaque models and clinical trials demonstrate efficacy of oral or topical antiretrovirals used prior to HIV exposure to prevent HIV transmission, ie pre-exposure prophylaxis (PrEP). Early initiation of effective HIV treatment in serodiscordant couples results in a 96% decrease in HIV transmission. HIV testing to determine serostatus and identify undiagnosed persons is foundational to these approaches. The relative efficacy of different approaches, adherence, cost and long-term safety will affect uptake and impact of these strategies. Ongoing research will help characterize the role for oral and topical formulations and help quantify potential benefits in sub-populations at risk for HIV acquisition.

New insights into the evolutionary rate of HIV-1 at the within-host and epidemiological levels

Over calendar time, HIV-1 evolves considerably faster within individuals than it does at the epidemic level. This is a surprising observation since, from basic population genetic theory, we would expect the genetic substitution rate to be similar across different levels of biological organization. Three different mechanisms could potentially cause the observed mismatch in phylogenetic rates of divergence: temporal changes in selection pressure during the course of infection; frequent reversion of adaptive mutations after transmission; and the storage of the virus in the body followed by the preferential transmission of stored ancestral virus. We evaluate each of these mechanisms to determine whether they are likely to make a major contribution to the mismatch in phylogenetic rates. We conclude that the cycling of the virus through very long-lived memory CD4(+) T cells, a process that we call 'store and retrieve', is probably the major contributing factor to the rate mismatch. The preferential transmission of ancestral virus needs to be integrated into evolutionary models if we are to accurately predict the evolution of immune escape, drug resistance and virulence in HIV-1 at the population level. Moreover, early infection viruses should be the major target for vaccine design, because these are the viral strains primarily involved in transmission.

Challenges for HIV pre-exposure prophylaxis among men who have sex with men in the United States

In light of recent research, Gordon Mansergh and colleagues discuss barriers to effective implementation of HIV pre-exposure prophylaxis for men who have sex with men.

Modeling dynamic interactions between pre-exposure prophylaxis interventions & treatment programs: predicting HIV transmission & resistance

Clinical trials have recently demonstrated the effectiveness of Pre-Exposure Prophylaxis (PrEP) in preventing HIV infection. Consequently, PrEP may soon be used for epidemic control. We model the dynamic interactions that will occur between treatment programs and potential PrEP interventions in resource-constrained countries. We determine the consequences for HIV transmission and drug resistance. We use response hypersurface modeling to predict the effect of PrEP on decreasing transmission as a function of effectiveness, adherence and coverage. We predict PrEP will increase need for second-line therapies (SLT) for treatment-naïve individuals, but could significantly decrease need for SLT for treatment-experienced individuals. If the rollout of PrEP is carefully planned it could increase the sustainability of treatment programs. If not, need for SLT could increase and the sustainability of treatment programs could be compromised. Our results show the optimal strategy for rolling out PrEP in resource-constrained countries is to begin around the "worst" treatment programs.

Pre-exposure prophylaxis and antiretroviral resistance: HIV prevention at a cost?

Pre-exposure prophylaxis (PrEP), the use of antiretrovirals (ARVs) by human immunodeficiency virus (HIV)-uninfected individuals to prevent acquisition of the virus during high-risk sexual encounters, enjoyed its first 2 major successes with the Centre for the AIDS Programme of Research in South Africa (CAPRISA) 004 and the Pre-Exposure Prophylaxis Initiative (iPrEx). These successes were buoyed by additional positive results from the TDF2 and Partners PrEP trials. Although no seroconverters in either arm of CAPRISA developed resistance to tenofovir, 2 participants in iPrEx with undetected, seronegative acute HIV infection were randomized to receive daily oral tenofovir-emtricitabine and resistance to emtricitabine was later discovered in both men. A similar case in the TDF2 study resulted in resistance to both ARVs. These cases prompted us to examine existing literature on the nature of resistance mutations elicited by ARVs used for PrEP. Here, we discuss the impact of signature mutations selected by PrEP, how rapidly these emerge with daily ARV exposure, and the individual-level and public health consequences of ARV resistance.

What do mathematical models tell us about the emergence and spread of drug-resistant HIV?

PURPOSE OF REVIEW

To discuss recent HIV epidemic models examining the transmission of antiretroviral (ARV) drug resistance.

RECENT FINDINGS

A relatively small number of recent transmission models have investigated ARV resistance in the context of therapeutic, combined ART (cART); ARV-vaginal microbicides (ARV-VMB); and oral pre-exposure prophylaxis (PrEP). Models of cART use have highlighted potential concerns about future resistance transmission, particularly in resource-constrained settings, and have emphasized the benefits of viral load monitoring in limiting resistance spread. PrEP models have concluded that inadvertent use by HIV-infected individuals could increase resistance prevalence, and that risk compensation by PrEP users could limit their beneficial effects on HIV transmission. ARV-VMB models have demonstrated that whereas resistance can reduce prophylactic effectiveness in preventing HIV acquisition of female ARV-VMB users, it may concomitantly benefit users' male partners if the resistant strains that female users acquire are less transmissible than wild-type strains. The models have examined the balance between these two factors at the population level.

SUMMARY

Recent HIV transmission models have adopted a wide assortment of structures and assumptions to explore drug resistance in the context of different ARV interventions in various settings. There is a need for future work emphasizing the simultaneous effects of multiple ARV interventions, as well as the public health impact of resistance, not just its prevalence.