For this project, we will further extend the previously
calibrated/validated simulation model of HIV among MSM in Baltimore to
incorporate explicit representation of rectal gonorrhea/chlamydia (NG/CT),
modeled as a single entity, in parallel to the existing model of HIV
transmission. NG/CT contribute to the increased risk and racial disparities in
HIV among MSM. We will explicitly and separately
model transmission of NG/CT through the Baltimore MSM population, accounting
for the fact that the selected STI will co-localize with HIV and will indeed
increase the transmission risk of HIV in individuals harboring the NG/CT. We
will calibrate the model to the estimated incidence and prevalence of NG/CT in
Baltimore’s MSM population, including co-localization with HIV and the fact
that, for many individuals, HIV infection is preceded/foreshadowed by infection
with NG/CT (thereby making infection with NG/CT a potential target for PrEP
initiation). We will use the model to demonstrate how NG/CT affects the
dynamics of HIV among Baltimore’s MSM population. We will then project the
potential impact of better STI care – including offering PrEP to individuals
diagnosed with NG/CT – on HIV transmission in the city.
The primary goal of this project is to use stochastic network modeling to estimate the proportion of HIV infections among MSM that are caused by prevalent STIs. HIV transmission in a dynamic sexual network of MSM will be modeled in the context of five STIs: urethral and rectal chlamydia, urethral and rectal gonorrhea, and syphilis. The proportion of HIV infections occurring among men with prevalent STI infection will be considered the population attributable fraction. Due to the uncertainty in estimates of transmission probabilities, we will conduct sensitivity analyses across a range of plausible values for increased susceptibility to HIV acquisition due to STI infection.
This study will examine the role of expedited partner therapy (EPT) for STI prevention among MSM by extending our HIV/STI modeling platform to include this new STI control technique for site-specific gonorrhea, chlamydia, and syphilis. EPT is not currently recommended for MSM by CDC and thus traditional epidemiological studies are not We propose an analysis to use this platform to test how EPT could be used alone and alongside other STI prevention interventions to reduce disease incidence.
In the proposed models, EPT will be simulated as the immediate provision of antibiotic medication to the current sexual partners of those MSM who are routinely diagnosed and treated for those STIs in clinical settings. Parameters in these models will include the coverage fraction for EPT (the proportion of MSM with EPT-indicated partners who accept it) and medication uptake among those partners. Sensitivity analyses for these models could explore how EPT targeted at STI-infected MSM with particular partnership configurations could maximize the epidemiological impact (infections averted) and efficiency (number needed to treat) of that intervention. With collaboration from DSTDP colleagues at CDC, these outcomes could be directly translated into a cost-effectiveness analysis comparing standard clinic-based testing and treatment of STIs versus EPT. The paper may also include an online web-based modeling tool that will allow STI program officials at local jurisdictions to explore the potential impact, efficiency, and cost-effectiveness of EPT to be integrated within their STI prevention programs. This will be based on the design and content of the web tool for our Year 2 paper [http://prism.shinyapps.io/cdc-prep-guidelines].
MSM in the United States are disproportionately affected by the STI epidemic. In previous work, we have demonstrated the efficacy of HIV preexposure prophylaxis (PrEP) for STI prevention thanks to the recommended STI screening process for PrEP users. Men who are eligible for PrEP engage in certain risk behaviors for both HIV and STI transmission, making them good candidates for targeted STI testing. There is a particular need for modeling the potential impact of various targeting and intervention programs on STI incidence in this key population. We extend our existing agent-based mathematical model of rectal and urogenital HIV and STD transmission to include syphilis with an aim to evaluate the effect of the current STD screening recommendations referenced in the CDC STI treatment guidelines and other potential targeting mechanisms on STI incidence for MSM.
Although these recommendations have been present for a long period of time, uptake of STI testing in this population has been suboptimal. Parameters in these models will include the coverage fraction for STI testing (the proportion of MSM with EPT-indicated partners who accept it) and adherence to recommended testing intervals. Sensitivity analyses for these models could explore the length of the recommended screening intervals for all sexually active and high-risk MSM, respectively, as well as potential definitions of “high-risk” that could maximize the epidemiological impact (infections averted) and efficiency (number needed to treat) of that intervention. With collaboration with DSTDP colleagues at CDC, we also aim to conduct an economic evaluation of these guidelines, appraising the economic impact of different recommended testing interval lengths.
Comparing the Effects of STI Prevention The goal of this project will be to extend the population attributable fraction (PAF) work to assess the potential impact of STI screening on HIV incidence. Specifically, this project merges two existing CAMP-supported projects: the PAF model and the STI guidelines model. We will assess the downstream effect of implementation of the STI guidelines on HIV incidence among MSM due to increased risk of HIV transmission and acquisition in the presence of prevalent STI. This work will include the effects of gonorrhea and chlamydia at a minimum. If we are able to overcome the challenges of incorporating syphilis into the model then we will also assess the effects of testing and screening for syphilis.
A major strategy for STI/HIV prevention has been network-based and partner-based targeting strategies for increasing screening, treatment, and linkage to other services. Disease intervention specialists (DIS) within health departments attempt to break onward STI transmission chains by offering treatment to a subset of named partners that may be contacted. While these DIS efforts have been successful in identifying and treating STIs, their population-level epidemiological impact and cost-effectiveness for men who have sex with men (MSM) has not been modeled robustly. In this modeling study, we will investigate these disease prevention approaches as used in the real world by local and state health departments. We will simulate the scale-up of DIS-based STI disease identification and treatment through sexual partnership networks of MSM. The goal will be to evaluate how DIS services may be optimally used compared to other potential STI testing and treatment approaches.
The goal of this project will be to extend the population attributable fraction (PAF) work to assess the cost-effectiveness of STI screening in terms of reducing HIV incidence. Specifically, this project merges two existing CAMP-supported projects: the PAF model and the STI guidelines model. We will assess the downstream effect of implementation of the STI guidelines on HIV incidence among MSM with respect to quality-adjusted life years (QALYs) gained under different STI testing scenarios.
The population-level prevention benefits of HIV PrEP will strongly depend on how the medication is used by those at substantial risk of infection. Questions remain about the potential of PrEP to achieve long-term reductions in HIV incidence among MSM given uncertainty about patterns of uptake, adherence, and discontinuation of the medication; these patterns will likely differ from the CDC’s clinical practice guidelines on PrEP indications and utilization. Deviations include: 1) the use of PrEP by MSM who self-select in using the medication but have no (or minimal) risk indications; 2) the non-use of PrEP by MSM with strong risk indications, based on either lack of awareness of PrEP or limited access to PrEP providers; 3) time-varying patterns of adherence (or non-adherence) to PrEP relative to time-varying patterns of high-risk sexual activity, compared to daily use recommended by CDC following FDA approval guidelines; and 4) heterogeneity in how MSM fully discontinue PrEP use unrelated to their ongoing risk indications, based on clinical, biological, or psychological reasons in stopping medication. In this study, we propose to build on the robust HIV PrEP implementation in our prior network-based simulation models to address questions of how longitudinal variation in these various factors could impact both the epidemiological impact and cost-effectiveness of HIV PrEP as a prevention intervention for MSM in the United States.
HIV testing is the cornerstone of HIV prevention. CDC recommends HIV testing at least annually for persons at risk of HIV infection. Previous modeling studies have suggested that HIV testing more frequently would be unlikely to be cost-effective at the population level. These models, however, did not incorporate the benefits of linkage to PrEP (soon after initiation of indicating risks) and immediate HIV treatment (for diagnosed infected persons) that would improve with increased testing. Our prior PrEP model also found that nearly half of at-risk MSM were missed by standard HIV testing frequencies that lead to PrEP evaluation. We propose to build on the existing model platform to investigate the HIV prevention benefits of a three-pronged strategy to reduce HIV incidence through: 1) more frequent diagnostic HIV testing; 2) immediate HIV treatment for persons with diagnosed acute and early HIV infection; and 3) PrEP for those who test negative but are at high risk. The project will evaluate the relative benefits of each of these components independently and in combination to identify the optimal mix of these strategies for both public health impact (number of infections averted) and efficiency (cost-effectiveness).
The primary goal of this project is to model the effect of different levels of PrEP coverage across strata of age, race, and geography. Risk screening tools have been found to perform deferentially by race, resulting in under-identification of black MSM with indications for PrEP. We propose to examine different scenarios of PrEP coverage in high-risk groups (e.g., offering PrEP to all black MSM under age 30) to assess the overall impact on HIV incidence at a national level.
In years 3 and 4, we developed a user-friendly transmission modeling tool designed to provide answers to the relationship between behavioral changes and STI incidence among US adolescents. This tool is heading into clearance and will then be publicly available. With this product, we propose to fulfill three aims:
1. Inform public health departments around the country about the existence of the tool, and provide guidance in its use.
2. Develop a case study that uses the tool to compare the projected impacts of a specific form of behavior change at the national level with that of a single jurisdiction, and interpret those results
3. Communicate to this audience the various unanticipated challenges we tackled on the development of the tool, and what they tell us about the state of STI surveillance and epidemiology for adolescents
We aim to complete all three of these aims through a manuscript and accompanying presentations/webinars/workshops of some form. Some remaining details of the case study and the dissemination methods are to be developed in consultation with DASH.
We propose to assess the impact of changes in risk behaviors among adolescents by race, based on a recent 10-year trend analysis of the YRBS. This analysis demonstrated significant reductions in risk behaviors (proportion of adolescents ever having sex, numbers of partners, those reporting being currently sexually active) among Black and Hispanic adolescents. On the other hand, it demonstrated decreased condom use among White adolescents. This project will project the levels of gonorrhea and chlamydia incidence over ten years in the absence of those changes, as well as the levels expected in their presence. Our analyses will focus on heterosexually active adolescents. We will project outcomes specific to race/ethnicity groups, and work with DASH partners to estimate the cost or savings associated with each outcome.
We propose to assess the impact of changes in risk behaviors among adolescents by race, based on a recent 10-year trend analysis of the YRBS. This analysis demonstrated significant reductions in risk behaviors (proportion of adolescents ever having sex, numbers of partners, those reporting being currently sexually active) among Black and Hispanic adolescents. On the other hand, it demonstrated decreased condom use among White adolescents. This project will project the numbers of pregnancy over ten years in the absence of those changes, as well as the numbers expected in their presence. Our analyses will focus on heterosexually active adolescents. We will project outcomes specific to race/ethnicity groups, and work with DASH partners to estimate the cost or savings associated with each outcome.