Introducing pre-exposure prophylaxis to prevent HIV acquisition among men who have sex with men in Sweden: insights from a mathematical pair formation model

A Review of Network Models for HIV Spread

BACKGROUND

HIV/AIDS has been a global health crisis for over 4 decades. Network models, which simulate human behavior and intervention impacts, have become an essential tool in guiding HIV prevention strategies and policies. However, no comprehensive survey of network models in HIV research has been conducted. This article fills that gap, offering a summary of past work and future directions to engage more researchers and inform policy related to eliminating HIV.

SETTING

Network models explicitly represent interactions between individuals, making them well-suited to study HIV transmission dynamics. Two primary modeling paradigms exist: a mechanistic approach from applied mathematics and a statistical approach from the social sciences. Each has distinct strengths and weaknesses, which should be understood for effective application to HIV research.

METHODS

We conducted a systematic review of network models used in HIV research, detailing the model types, populations, interventions, behaviors, datasets, and software used, while identifying potential future research directions.

RESULTS

Network models are particularly valuable for studying behaviors central to HIV transmission, such as partner selection and treatment adherence. Unlike traditional models, they focus on individual behaviors, aligning them with clinical practice. However, more accurate network data are needed for better model calibration and actionable insights.

CONCLUSIONS

This article serves as a point of reference for HIV researchers interested in applying network models and understanding their limitations. To our knowledge, this is the most comprehensive review of HIV network models to date.

Low clinical impact of HIV drug resistance mutations in oral pre-exposure prophylaxis: a systematic review and meta-analysis

INTRODUCTION

Despite the widespread use of pre-exposure prophylaxis (PrEP) in preventing human immunodeficiency virus (HIV) transmission, scant information on HIV drug resistance mutations (DRMs) has been gathered over the past decade. This review aimed to estimate the pooled prevalence of pre-exposure prophylaxis and its two-way impact on DRM.

METHODS

We systematically reviewed studies on DRM in pre-exposure prophylaxis according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis 2020 guidelines. PubMed, Cochrane, and SAGE databases were searched for English-language primary studies published between January 2001 and December 2023. The initial search was conducted on 9 August 2021 and was updated through 31 December 2023 to ensure the inclusion of the most recent findings. The registration number for this protocol review was CRD42022356061.

RESULTS

A total of 26,367 participants and 562 seroconversion cases across 12 studies were included in this review. The pooled prevalence estimate for all mutations was 6.47% (95% Confidence Interval-CI 3.65-9.93), while Tenofovir Disoproxil Fumarate/Emtricitabine-associated drug resistance mutation prevalence was 1.52% (95% CI 0.23-3.60) in the pre-exposure prophylaxis arm after enrolment. A subgroup analysis, based on the study population, showed the prevalence in the heterosexual and men who have sex with men (MSM) groups was 5.53% (95% CI 2.55-9.40) and 7.47% (95% CI 3.80-12.11), respectively. Notably, there was no significant difference in the incidence of DRM between the pre-exposure prophylaxis and placebo groups (log-OR = 0.99, 95% CI -0.20 to 2.18, I2 = 0%; p = 0.10).

DISCUSSION

Given the constrained prevalence of DRM, the World Health Organization (WHO) advocates the extensive adoption of pre-exposure prophylaxis. Our study demonstrated no increased risk of DRM with pre-exposure prophylaxis (p > 0.05), which is consistent with these settings. These findings align with the previous meta-analysis, which reported a 3.14-fold higher risk in the pre-exposure prophylaxis group than the placebo group, although the observed difference did not reach statistical significance (p = 0.21).

CONCLUSIONS

Despite the low prevalence of DRM, pre-exposure prophylaxis did not significantly increase the risk of DRM compared to placebo. However, long-term observation is required to determine further disadvantages of extensive pre-exposure prophylaxis use. PROSPERO Number: CRD42022356061.

Estimating Partnership Duration among MSM in Belgium-A Modeling Study

Mathematical modeling is widely used for describing infection transmission and evaluating interventions. The lack of reliable social parameters in the literature has been mentioned by many modeling studies, leading to limitations in the validity and interpretation of the results. Using data from the European MSM Internet survey 2017, we developed a network model to describe sex acts among MSM in Belgium. The model simulates daily sex acts among steady, persistent casual and one-off partners in a population of 10,000 MSM, grouped as low- or high-activity by using three different definitions. Model calibration was used to estimate partnership duration and homophily rates to match the distribution of cumulative sex partners over 12 months. We estimated an average duration between 1065 and 1409 days for steady partnerships, 4-6 and 251-299 days for assortative high- and low-activity individuals and 8-13 days for disassortative persistent casual partnerships, respectively, varying across the three definitions. High-quality data on social network and behavioral parameters are scarce in the literature. Our study addresses this lack of information by providing a method to estimate crucial parameters for network specification.

The effect of PrEP uptake and adherence on the spread of HIV in the presence of casual and long-term partnerships

A model with both casual and long-term partnerships is considered with respect to the impact of a pre-exposure prophylaxis (PrEP) on the spread of HIV. We consider the effect of the effectiveness of PrEP, the rate that susceptible individuals choose to take PrEP, and compliance with the daily dose of the pre-exposure prophylaxis. The rate of infection in long-term partnerships is computed using a linearized expected value as a means for including the nonlocal effects of long-term partnerships while maintaining computational feasibility. The reproduction numbers for models with casual partnerships, long-term partnerships, and a combination of both are analytically computed and global stability of both disease-free and endemic equilibria is shown. Sensitivity and PRCC analysis results suggest that increasing the compliance among the current PrEP users is a more effective strategy in the fight against the HIV epidemic than increased coverage with poor compliance. Furthermore, an analysis of the reproduction number shows that models with either casual or monogamous long-term partnerships can reach the desired $ R_0 < 1 $ threshold for high enough levels of compliance and uptake, however, a model with both casual and monogamous long-term partnerships will require additional interventions. Methods highlighted in this manuscript are applicable to other incurable diseases or diseases with imperfect vaccines effected by long-term partnerships.

Non-selective distribution of infectious disease prevention may outperform risk-based targeting

Epidemic control often requires optimal distribution of available vaccines and prophylactic tools, to protect from infection those susceptible. Well-established theory recommends prioritizing those at the highest risk of exposure. But the risk is hard to estimate, especially for diseases involving stigma and marginalization. We address this conundrum by proving that one should target those at high risk only if the infection-averting efficacy of prevention is above a critical value, which we derive analytically. We apply this to the distribution of pre-exposure prophylaxis (PrEP) of the Human Immunodeficiency Virus (HIV) among men-having-sex-with-men (MSM), a population particularly vulnerable to HIV. PrEP is effective in averting infections, but its global scale-up has been slow, showing the need to revisit distribution strategies, currently risk-based. Using data from MSM communities in 58 countries, we find that non-selective PrEP distribution often outperforms risk-based, showing that a logistically simpler strategy is also more effective. Our theory may help design more feasible and successful prevention.

Pre-exposure prophylaxis (PrEP) is an effective HIV prevention measure but identifying those most at risk to target for treatment is challenging. Here, the authors demonstrate that non-selective PrEP distribution outperforms targeted strategies when use is not consistent, and/or prevalence of untreated HIV is high.

A comparison of attitudes and knowledge of pre-exposure prophylaxis (PrEP) between hospital and Key Population Led Health Service providers: Lessons for Thailand's Universal Health Coverage implementation

BACKGROUND

HIV Pre-exposure prophylaxis (PrEP) has demonstrated efficacy and effectiveness among high-risk populations. In Thailand, PrEP has been included in the National Guidelines on HIV/AIDS Treatment and Prevention since 2014. As a part of the national monitoring and evaluation framework for Thailand's universal coverage inclusion, this cross-sectional survey was conducted to assess knowledge of, attitudes to and practice (KAP) of PrEP service providers in Thailand.

METHODS

We conducted a cross-sectional survey to explore knowledge of, and attitudes towards PrEP among providers from hospital and Key Population Led Health Services (KPLHS) settings. The questionnaire was distributed online in July 2020. Descriptive and univariate analysis using an independent-sample t-test were applied in the analyses. Attitudes were ranked from the most negative (score of 1) to the most positive (score of 5).

RESULTS

Overall, there were 196 respondents (158 from hospitals and 38 from KPLHS) in which most hospital providers are female nurse practitioners while half of those from KPLHS report current gender as gay. Most respondents report a high level of PrEP knowledge and support provision in all high-risk groups with residual concern regarding anti-retroviral drugs resistance. Over two-fifths of providers from both settings perceive that PrEP would result in risk compensation and half of KPLHS providers are concerned regarding risk of sexual transmitted infections. Limited PrEP counselling time is a challenge for hospital providers.

CONCLUSIONS

Service integration between both settings, more involvement and distribution of KPLHS in reaching key populations would be essential in optimizing PrEP uptake and retention. Continuing support particularly in raising awareness about PrEP among healthcare providers and key populations, facilities and manpower, unlimited quota of patient recruitment and PrEP training to strengthen providers' confidence and knowledge would be essential for successful PrEP implementation.

Can HIV epidemics among MSM be eliminated through participation in preexposure prophylaxis rollouts?

OBJECTIVE

To study the conditions under which preexposure prophylaxis (PrEP) coverage can eliminate HIV among MSM in the Paris region.

DESIGN

Mathematical modeling.

METHODS

We propose an innovative approach, combining a transmission model with a game-theoretic model, for decision-making about PrEP use. Individuals at high risk of HIV infection decide to use PrEP, depending on their perceived risk of infection and the relative cost of using PrEP versus antiretroviral treatment (ART), which includes monetary and/or nonmonetary aspects, such as price and access model of PrEP, consequences of being infected and lifelong ART.

RESULTS

If individuals assessed correctly their infection risk, and the cost of using PrEP were sufficiently low, then the PrEP rollout could lead to elimination. Specifically, assuming 86% PrEP effectiveness, as observed in two clinical trials, a minimum PrEP coverage of 55% [95% confidence interval (CI) 43-64%] among high-risk MSM would achieve elimination in the Paris region. A complete condom drop by MSM using PrEP slightly increases the minimum PrEP coverage required for elimination, by ∼1%, whereas underestimation of their own HIV infection risk would require PrEP programs reduce the cost of using PrEP by a factor ∼2 to achieve elimination.

CONCLUSION

Elimination conditions are not yet met in the Paris region, where at most 47% of high-risk MSM were using PrEP as of mid-2019. Further lowering the cost of PrEP and promoting a fair perception of HIV risk are required and should be maintained in the long-run, to maintain elimination status.

HIV Pre-exposure Prophylaxis in the LGBTQ Community: A Review of Practice and Places

One in six bisexual and gay men will be diagnosed with HIV in their lifetime (Human Rights Campaign, 2017). Without a vaccine or cure, prevention may be the best tool to control the HIV pandemic. Since 2012, the World Health Organization (WHO) recommends HIV pre-exposure prophylaxis (PrEP) for a high-risk population. To this day, in the United States (U.S.), the group with the highest risk is MSM (men who have sex with other men) that have condom-less sexual intercourse (Center for Disease Control and Prevention, 2019). In fact, in 2018, over 50% of all HIV infections occurred in MSM and members of the LGBT community. A systematic review was conducted using PubMed, Google Scholar, and Cochrane Library. The inclusive criteria were articles published from 2015-2020, focusing specifically on HIV PrEP among the members of the LGBTQ+ community. The keywords for our search were "Pre-exposure prophylaxis," "HIV," "men who have sex with other men" (MSM), "Bisexual," "transgender." A total of 25 articles met the inclusion criteria. About 50% of the articles focused on MSM while others highlighted bisexual and transgender women. Globally, PrEP is a priority. Programs to educate and promote its use are being developed, but challenges are present regarding access to PrEP and its maintenance for longer than 12 months. In the U.S., PrEP programs started in 2012, intending to promote and educate. Research shows that more than 60% of the high-risk patients are willing to try PrEP if they are correctly educated, showing that physicians were not doing a thorough job educating their patients. PrEP is essential for preventing the transmission of HIV among the LGBTQ+ subpopulation. Existing gaps need to be bridged to create or improve to educate high-risk populations and physicians on HIV PrEP.

Mathematical modelling of the influence of serosorting on the population-level HIV transmission impact of pre-exposure prophylaxis

OBJECTIVES

HIV pre-exposure prophylaxis (PrEP) may change serosorting patterns. We examined the influence of serosorting on the population-level HIV transmission impact of PrEP, and how impact could change if PrEP users stopped serosorting.

DESIGN

We developed a compartmental HIV transmission model parameterized with bio-behavioural and HIV surveillance data among MSM in Canada.

METHODS

We separately fit the model with serosorting and without serosorting [counterfactual; sero-proportionate mixing (random partner-selection proportional to availability by HIV status)], and reproduced stable HIV epidemics with HIV-prevalence 10.3-24.8%, undiagnosed fraction 4.9-15.8% and treatment coverage 82.5-88.4%. We simulated PrEP-intervention reaching stable pre-specified coverage by year-one and compared absolute difference in relative HIV-incidence reduction 10 years post-intervention (PrEP-impact) between models with serosorting vs. sero-proportionate mixing; and counterfactual scenarios when PrEP users immediately stopped vs. continued serosorting. We examined sensitivity of results to PrEP-effectiveness (44-99%; reflecting varying dosing or adherence levels) and coverage (10-50%).

RESULTS

Models with serosorting predicted a larger PrEP-impact than models with sero-proportionate mixing under all PrEP-effectiveness and coverage assumptions [median (interquartile range): 8.1% (5.5-11.6%)]. PrEP users' stopping serosorting reduced PrEP-impact compared with when PrEP users continued serosorting: reductions in PrEP-impact were minimal [2.1% (1.4-3.4%)] under high PrEP-effectiveness (86-99%); however, could be considerable [10.9% (8.2-14.1%)] under low PrEP effectiveness (44%) and high coverage (30-50%).

CONCLUSION

Models assuming sero-proportionate mixing may underestimate population-level HIV-incidence reductions due to PrEP. PrEP-mediated changes in serosorting could lead to programmatically important reductions in PrEP-impact under low PrEP-effectiveness. Our findings suggest the need to monitor sexual mixing patterns to inform PrEP implementation and evaluation.

How perceived Australian sexual norms shape sexual practices of East Asian and sub-Saharan African international students in Sydney

INTRODUCTION

Sexual norms, real or perceived, shape young people's sexual behaviour and may constitute one of the greatest challenges in HIV/STIs prevention among this population. This study used sexual script theory to explore how international students in Sydney, Australia - from traditional cultures of East Asian and sub-Saharan African countries - construct home backgrounds and Australian sexual norms and how this may shape their sexual practices during their studies in Australia.

METHODS

The study involved face-to-face and telephone semi-structured in-depth interviews. Data were provided by 20 international students who are enrolled in various universities in Sydney. Interviews were audio-recorded, transcribed, coded into NVivo and analysed using reflexive thematic analysis.

RESULTS

Identified patterns in the data showed three themes through which participants perceive sexual norms in Australia as distinctly different from their home country norms. First, participants stated that unlike their home country norms, sexual norms in Australia are permissive. Second, participants hold the view that compared to their home country norms, sex in Australia is largely casual as it is not always attached to love. Some participants revealed that this could shape their own sexual practices during their studies in Australia. Finally, participants noted that compared to their home countries' norm of sex talk taboo, Australia has an open sexual communication norm; which they believe, enables young people in western societies to easily acquire sexual health information.

CONCLUSIONS

Findings provide evidence to support a need for contextualized and effective sexual health services for international students that take account of perceptions around sexual norms and how they can be modified to ensure that sexual practices which these students may engage in, will be managed in a safe and responsible manner.