A complex systems approach to evaluate HIV prevention in metropolitan areas: preliminary implications for combination intervention strategies.

Brandon D L Marshall,Lars Seemann,Sandro Galea,Barbara Tempalski,Samuel R Friedman,Enrique R Pouget,Magdalena M Paczkowski

doi:10.1371/journal.pone.0044833

Abstract

BackgroundHIV transmission among injecting and non-injecting drug users (IDU, NIDU) is a significant public health problem. Continuing propagation in endemic settings and emerging regional outbreaks have indicated the need for comprehensive and coordinated HIV prevention. We describe the development of a conceptual framework and calibration of an agent-based model (ABM) to examine how combinations of interventions may reduce and potentially eliminate HIV transmission among drug-using populations.Methodology/Principal FindingsA multidisciplinary team of researchers from epidemiology, sociology, geography, and mathematics developed a conceptual framework based on prior ethnographic and epidemiologic research. An ABM was constructed and calibrated through an iterative design and verification process. In the model, “agents” represent IDU, NIDU, and non-drug users who interact with each other and within risk networks, engaging in sexual and, for IDUs, injection-related risk behavior over time. Agents also interact with simulated HIV prevention interventions (e.g., syringe exchange programs, substance abuse treatment, HIV testing) and initiate antiretroviral treatment (ART) in a stochastic manner. The model was constructed to represent the New York metropolitan statistical area (MSA) population, and calibrated by comparing output trajectories for various outcomes (e.g., IDU/NIDU prevalence, HIV prevalence and incidence) against previously validated MSA-level data. The model closely approximated HIV trajectories in IDU and NIDU observed in New York City between 1992 and 2002, including a linear decrease in HIV prevalence among IDUs. Exploratory results are consistent with empirical studies demonstrating that the effectiveness of a combination of interventions, including syringe exchange expansion and ART provision, dramatically reduced HIV prevalence among IDUs during this time period.Conclusions/SignificanceComplex systems models of adaptive HIV transmission dynamics can be used to identify potential collective benefits of hypothetical combination prevention interventions. Future work will seek to inform novel strategies that may lead to more effective and equitable HIV prevention strategies for drug-using populations.

Highlights

The global incidence of human immunodeficiency virus (HIV) infection has declined by over 20% since its peak in 1997, the persistent large number of new infections annually, estimated at 2.6 million in 2009 [1], demonstrates that the need for effective HIV prevention strategies remains urgent
We have focused our initial modeling efforts on four programs (i.e., needle and syringe exchange program (NSP), substance abuse treatment, voluntary counseling and HIV testing (VCT), and highly active antiretroviral therapy (HAART)) which are described by the World Health Organization (WHO)/United Nations Programme on HIV/AIDS (UNAIDS)/United Nations Office on Drugs and Crime (UNODC) as ‘‘core interventions’’ within a comprehensive package of HIV-related services for drug users [42]
To obtain the per-partner probability of HIV transmission between serodiscordant agents, we model a series of Bernoulli distributions, ppartner = 1– (1– pact)n, where ppartner is the annualized per partnership risk of HIV transmission, pact is the per act ‘‘transmission event’’ probability described above, and n is the number of ‘‘trials’’ per partnership per time step

Summary

Introduction

The global incidence of HIV infection has declined by over 20% since its peak in 1997, the persistent large number of new infections annually, estimated at 2.6 million in 2009 [1], demonstrates that the need for effective HIV prevention strategies remains urgent. A series of recently published efficacious interventions [2,3,4] have renewed interest in placing prevention-centered approaches at the center of global HIV elimination strategies. We will adopt the term ‘‘highly active HIV prevention’’ to refer to the additive (and potentially interactive) effect of combining treatment-centered approaches, biomedical strategies, behavioral interventions, and structural changes to suppress and eventually eliminate HIV transmission [10]. HIV transmission among injecting and non-injecting drug users (IDU, NIDU) is a significant public health problem. We describe the development of a conceptual framework and calibration of an agent-based model (ABM) to examine how combinations of interventions may reduce and potentially eliminate HIV transmission among drug-using populations

Methods

Results

Conclusion