Impact of Providing Preexposure Prophylaxis for Human Immunodeficiency Virus at Clinics for Sexually Transmitted Infections in Baltimore City: An Agent-based Model

Abstract

Background: Preexposure prophylaxis (PrEP) greatly reduces the risk of human immunodeficiency virus (HIV) acquisition, but its optimal delivery strategy remains uncertain. Clinics for sexually transmitted infections (STIs) can provide an efficient venue for PrEP delivery.

Methods: To quantify the added value of STI clinic-based PrEP delivery, we used an agent-based simulation of HIV transmission among men who have sex with men (MSM). We simulated the impact of PrEP delivery through STI clinics compared with PrEP delivery in other community-based settings. Our primary outcome was the projected 20-year reduction in HIV incidence among MSM.

Results: Assuming PrEP uptake and adherence of 60% each, evaluating STI clinic attendees and delivering PrEP to eligible MSM reduced HIV incidence by 16% [95% uncertainty range, 14%-18%] over 20 years, an impact that was 1.8 (1.7-2.0) times as great as that achieved by evaluating an equal number of MSM recruited from the community. Comparing strategies where an equal number of MSM received PrEP in each strategy (ie, evaluating more individuals for PrEP in the community-based strategy, because MSM attending STI clinics are more likely to be PrEP eligible), the reduction in HIV incidence under the STI clinic-based strategy was 1.3 (1.3-1.4) times as great as that of community-based delivery.

Conclusions: Delivering PrEP to MSM who attend STI clinics can improve efficiency and effectiveness. If high levels of adherence can be achieved in this population, STI clinics may be an important venue for PrEP implementation.

Figure 1:. Simulation overview.

This figure illustrates the schematic simulation logic for modeling HIV natural history and the cascade of care (top panel), individuals’ presentation to STI clinics (middle panel) and PrEP procedure (bottom panel). Top Panel: HIV natural history is modeled through 3 main disease states associated with an increase in viral load (with parameters given in Table 1). The cascade of care – also evaluated on a weekly basis – represents processes of diagnosis, linkage to care, ART initiation, and retention in care. Middle panel: “Eligibility” for presenting to an STI clinic is evaluated at the end of each week: individuals have a defined probability of presenting to an STI clinic during any week in which they start a new partnership or their stable partner starts a concurrent partnership. Bottom panel: MSM are selected for PrEP assessment at the time of attending STI-clinics (strategy 1), or randomly from the community at large (strategy 2). The eligibility criteria for PrEP are set according to CDC guidelines. Eligible MSM who accept PrEP (according to PrEP “uptake”) initiate PrEP immediately and will experience a fixed level of protection against HIV transmission (“adherence”) while on PrEP.

Figure 2:. Impact of STI clinic-based versus community-based PrEP delivery.

Shown on the y-axes are the projected annual number of MSM screened for PrEP (A), initiating PrEP (B), and receiving PrEP (C) in a given year, as well as the projected reduction in HIV incidence (D), reduction in HIV prevalence (E), and the relative impact of STI clinic-based PrEP versus community-based PrEP on HIV incidence at 20 years (F). For Panels A through E, the quantities are shown in each year after enacting a PrEP campaign of sufficient size to evaluate all MSM estimated to present to the STI clinic every year (966 visits per year, red line), a comparable number of MSM randomly screened for PrEP every year (green line), or a comparable number of eligible MSM randomly starting PrEP (blue line) in any given week of the program. Thus, in Panel A, the red and green lines overlap (equal number of MSM screened for PrEP every year), and in Panel B, the red and blue lines overlap (equal number initiating PrEP every year). Panel F depicts the relative impact of STI clinic-based PrEP versus community-based PrEP, measured as the projected reduction in HIV incidence at the 20^th year of implementation. These figures assume 60% PrEP uptake and 60% adherence to PrEP once initiated. STI, sexually transmitted infection; PrEP, pre-exposure prophylaxis for HIV.

Figure 3:. Sensitivity analysis of the impact of STI clinic-based PrEP delivery on HIV incidence according to uptake and adherence.

Panel A shows the percent reduction in HIV incidence after 20 years of STI clinic-based PrEP delivery, as a function of PrEP uptake (on the x-axis) and adherence (on the y-axis, modeled as the percentage of days with immunity to HIV infection). Panel B represents the relative impact of an STI clinic-based PrEP delivery strategy over community-based PrEP, assuming equal levels of screening (equivalent to the green scenarios in Figure 2).