To the Editor: Human immunodeficiency virus (HIV) transmission among injecting drug users (IDUs) is commonly attributed to the practice of sharing contaminated needles and syringes(1). The minimal infectious dose of HIV is unknown, but the volume of innoculum and quantity of virus in an exposure are believed to influence the risk of transmission (2-5). Both factors may be affected by the type of syringe used by an IDU. As an ethnographer (1989-92) and IDU (1968-87), one author (WZ) observed a change in syringes used by IDUs in Texas during the HIV epidemic. Syringes in current use have permanently attached needles and retain visibility less fluid and blood than syringes with detachable needles used previously. Prior studies (6-8) have quantified the amount of blood in needle and syringe sharing simulations; the type of needle, detachable or integral cannula (permanently attached), was not specified. Only one study (8) incorporated the practice, common among IDUs, of rinsing with water between uses. We measured differences in fluid and blood retained in needle and syringe combinations in a series of experiments.
