Proactive syringe services programs decrease the incidence of HIV infection more than the implementation of reactive syringe services programs, according to a study published in Clinical Infectious Diseases.

Worldwide, there are approximately 3 million people living with HIV who inject drugs. Although success has been achieved at reducing HIV transmission in some settings, there have still been outbreaks in recent years. These outbreaks have been associated with factors such as limited access to sterile injection equipment and other harm-reduction services, including syringe services programs. The largest HIV outbreak in Indiana’s Scott County occurred in 2015 with 181 people diagnosed with HIV in one year in a rural community of 24,000. This outbreak was a result of high-frequency injection of oxymorphone and was declared a public health emergency. Before this declaration, there were limited syringe services programs available, but within 1 week, the first legal syringe services programs were opened in Indiana. However, it is estimated that 80% of infections occurred prior to the declaration of injection of oxymorphone as a public health emergency, and it is suggested that if these resources were available earlier, the outbreak might have been prevented. Therefore, this study estimated the benefits of preexisting and reactive syringe services programs implementation on HIV transmission in a virtual population that mimicked a rural county in the United States using an agent-based model.

A virtual population simulated HIV transmission for 5 years in a population of 24,110 residents in a rural county in the United States using an agent-based model after 1 infection was introduced. Agent-based modeling is used to understand how macrolevel phenomena are generated and influenced by microlevel interactions. Within this virtual population, the prevalence of injection drug use was 1.7% and syringe sharing occurred in 34% of all injection events. In scenarios where syringe services programs were implemented, 55% of people who injected drugs used the services. The primary outcome was HIV incidence and the associated percent reduction relative to the base scenario.

Over the simulated 5 years, this model predicted 210 infections, or an incidence of 0.18 infections per 100 person-years in the absence of syringe services programs, which resulted in a prevalence of 0.96%. The majority of these infections were among people who injected drugs. When narrowed to the population of people who injected drugs, the incidence rose to 12.1 (176 infections) per 100 person-years. When proactive syringe services programs were implemented, the incidence was decreased by 90.3%, with 154 infections averted. However, with reactive implementation that began 10 months after the first infection, syringe services programs were predicted to decrease the incidence by 60.8%, with 107 infections averted. Similar reductions were also seen among people who did not inject drugs.

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These results suggest that proactive syringe services programs implementation in Scott County may have prevented more HIV infections than the reactive syringe services programs implementation. Overall, the study authors concluded that, “Consequently, there is a need for expanded proactive [syringe services programs] implantation in the context of enhanced monitoring of outbreak vulnerability in Scott County and in similar rural contexts.”

Reference

Goedel WC, King MR, Lurie MN, et al. Implantation of syringe services programs to prevent human immunodeficiency virus transmission in rural counties in the United States: a modeling study [published online May 30, 2019]. Clin Infect Dis. doi:10.1093/cid/ciz321