Abstract
BackgroundPeople who inject drugs (PWID) are at continued risk for HIV in the U.S., and experience disparities across the HIV care continuum compared to other high-risk groups. Estimates of the risk of HIV transmission at each stage of the care continuum may assist in identifying public health priorities for averting incident infections among PWID, in addition to transmissions to sexual partners of PWID.MethodsWe created an agent-based model simulating HIV transmission and the HIV care continuum for PWID in New York City (NYC) in 2012. To account for sexual transmission arising from PWID to non-PWID, the simulation included the entire adult NYC population. Using surveillance data and estimates from the National HIV Behavioral Surveillance system, we simulated a dynamic sexual and injecting network. We estimated the proportion of HIV transmission events attributable to PWID in the following categories, those: without an HIV diagnosis (‘Undiagnosed’); diagnosed but not on antiretroviral therapy (ART) (‘Diagnosed − not on ART’); those who initiated ART but were not virally suppressed (‘Unsuppressed’); and, those who achieved viral suppression (‘Suppressed’).ResultsWe estimated HIV incidence among PWID to be 113 per 100,000 person-years in 2012, with an overall incidence rate for the entire adult NYC population of 33 per 100,000 person-years. Despite accounting for only 33% of the HIV-infected PWID population, the Undiagnosed were associated with 52.6% (95% simulation interval [95% SI]: 47.1–57.0%) of total transmission events. The Diagnosed − not on ART population contributed the second-largest proportion of HIV transmissions, with 36.6% (95% SI: 32.2–41.5%). The Unsuppressed population contributed 8.7% (95% SI: 5.6–11.8%), and Suppressed 2.1% (95% SI: 1.1–3.9%), relatively little of overall transmission.ConclusionsAmong PWID in NYC, more than half (53%) of transmissions were from those who were unaware of their infection status and more than 36% were due to PWID who knew their status, but were not on treatment. Our results indicate the importance of early diagnosis and interventions to engage diagnosed PWID on treatment to further suppress population-level HIV transmission. Future HIV prevention research should focus on the elimination of identified and potential barriers to the testing, diagnosis, and retention of PWID on HIV treatment.
Highlights
People who inject drugs (PWID) are at continued risk for HIV in the U.S, and experience disparities across the HIV care continuum compared to other high-risk groups
A crucial element of HIV prevention for PWID is the use of antiretroviral therapy (ART) in reducing the infectiousness of HIV-infected individuals [7], in what is known as treatment as prevention (TasP)
Prevalence and frequency of HIV risk behaviors were estimated using an array of empirical studies and reports among PWID, men who have sex with men (MSM), and the general population; most notable among these were reports published by the National HIV Behavioral Surveillance (NHBS) system conducted by the Centers for Disease Control and Prevention (CDC) [18,19,20]
Summary
People who inject drugs (PWID) are at continued risk for HIV in the U.S, and experience disparities across the HIV care continuum compared to other high-risk groups. Settings such as New York City (NYC) and Vancouver have achieved dramatic reductions in HIV incidence among people who inject drugs (PWID), through efforts including needle and syringe programs and HIV treatment scale-up [2], indicating progress for HIV prevention in high-resource settings. Despite this progress, recent outbreaks have illustrated the need for expanded efforts to prevent HIV transmission among PWID [3, 4], as the use of some injection drugs, such as heroin, has increased in the U.S [5, 6]. A heuristic has evolved, described as the “HIV care cascade” or “continuum”, which delineates the steps needed to transform an HIV-infected population from being treatment-naïve and infectious to virologically suppressed on highly active antiretroviral therapy, wherein they are functionally unlikely to transmit HIV to new partners [12]
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