AIDSImpact.com:: - Santa Fe, USA 2011

Abstract #200 - HIV prevention among injecting drug users: focusing on the needle is missing the point
Authors: Presenting Author: Dr. William Zule - RTI International
Additional Authors:
Aim: To increase awareness regarding the potential impact of syringe design on the epidemiology and prevention of HIV among injecting drug users (IDUs). This presentation is particularly intended for policy makers, needle and syringe program operators and researchers who are interested in understanding and preventing HIV transmission among IDUs.
Method / Issue: When the plunger is fully-depressed, all syringes retain some fluid in what has been termed “dead space.” With the plunger depressed, high dead space syringes (HDSS) retain fluid in the tip of the syringe, the hub of the needle and the needle itself. Low dead space syringes (LDSS) have a needle that extends through the tip of the syringe to the base of the barrel. With the plunger depressed, LDSS retain fluid only in the needle itself. These differences in syringe design influence the volume of blood and HIV viral burden (i.e. viral burden = viral load x volume of inoculum) that may be transferred. HIV viral burden in an exposure is a primary determinant of the probability of HIV infection associated with the exposure. This presentation reviews evidence from laboratory studies, bio-behavioral surveys, mathematical models, and ecological studies on the differential impact of high and low dead space syringes on the distribution of HIV and hepatitis C virus (HCV) infection among IDUs.
Results / Comments: In laboratory studies that measured dead space in HDSS and LDSS, HDSS retained a mean of 84 µl of fluid and LDSS retained a mean of 2 µl of fluid. In experiments that simulated the injection process followed by two 0.5 ml rinses with water, HDSS retained approximately 1 µl of blood while LDSS retained < 0.001 µl of blood. In other laboratory experiments, researchers were able to culture HIV from HDSS with and without visible blood. However, they were unable to culture HIV from LDSS that did not contain visible blood. In another laboratory study, HCV survived up to 60 days in HDSS, but it only survived one day in LDSS. In bio-behavioral surveys that distinguished between using and sharing HDSS and LDSS, a history of sharing HDSS, but not LDSS, was associated with prevalent HIV and HCV Infection. In mathematical models, in high risk IDU populations HIV prevalence increased rapidly if they were using HDSS, but HIV epidemics did not occur in high risk IDU populations if fewer than 5% were using HDSS. An ecological study of HIV prevalence among IDUs and the types of syringes that they were using in over 60 cities across Europe and Asia found evidence that HDSS were used in every city where HIV prevalence exceeded 6%.
Discussion: Small things may make a big difference. Evidence from diverse sources suggests that LDSS may mediate the relationship between syringe sharing and HIV transmission. Given the biological plausibility and the existing evidence, questions regarding syringe type should be standard on HIV behavioral risk surveys of IDUs. Needle and syringe programs should offer LDSS and strongly encourage IDUs to use them. Policy makers should consider strategies for increasing the availability of LDSS.
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