Study shows potential impact of syringe type on injection-related HIV epidemics among drug users

Syringe type affects HIV transmission among intravenous drug users, according to a study by researchers at RTI International.

The study, published online in Addiction, used a mathematical model to illustrate the potential impact of syringe type on injection-related HIV epidemics in low- and high-risk intravenous drug user populations.

According to the authors, when a plunger on a syringe is fully depressed, all syringes retain fluid in what has been termed "dead space." In high dead-space syringes, which usually have detachable needles, more than 1000 times more blood is retained in the syringe after washing than in low dead-space syringes.

The researchers found that even a small percentage of exposures involving high dead-space syringes can increase the spread of HIV dramatically, especially in high-risk populations.

Conversely, the study showed that injection-related HIV epidemics are likely to be controlled in areas or populations where 95 percent of syringe-sharing episodes use low dead-space syringes.

"The results of our simulations may help explain the large geographic differences in HIV prevalence among intravenous drug users," said Georgiy Bobashev, Ph.D., a senior research statistician at RTI and the paper's lead author. "These differences have been observed but not explained adequately by differences in risk behaviors."

The authors said that although most intravenous drug users in the United States use low dead-space syringes, research has shown that some users in the United States continue to use high dead-space syringes.

"Our results demonstrate that syringe exchange programs and others involved in providing HIV prevention services to intravenous drug users may wish to consider providing low dead-space syringes to drug users as a potential HIV harm-reduction measure," said William Zule, Dr.P.H., a senior research health analyst at RTI and the paper's co-author. "However, providers need to be sure that the syringes they distribute meet the needs of local drug users. For example, distributing 1-milliliter low dead-space syringes to drug users who inject 5-milliliters of fluid at a time is likely to be ineffective."