These practices include frontloading (removing the needle from one syringe and filling that syringe by inserting the needle from another drug-filled syringe directly into the barrel), and backloading (removing the plunger from the back of the syringe and filling that syringe through the back with drugs from a second syringe). Studies of these factors have to date yielded conflicting results, with a report from New York finding a positive association between frontloading and HIV seroprevalence (Jose et al., 1992), and a study in Baltimore (Samuels et al., 1991) reporting similar seroprevalence rates for injection drug users who did and did not practice frontloading. Samuels and colleagues noted, however, that these results do not mean "that the behaviors are without risk of HIV infection among [injection drug users] … (but) that the associated risks are probably low relative to other (HIV risk) behaviors."

Impact of Bleach Disinfection on HIV Transmission

If disinfection of injection equipment is an effective means of preventing HIV infection, then HIV seroconversion rates would be expected to be lower among injection drug users who consistently disinfect their injection equipment. Prior to the initiation of the original CHOW program in San Francisco, Chaisson and colleagues (1987) found no protective effect for those injection drug users who reported cleaning their needles and syringes with boiling water or alcohol. Later, Moss and Chaisson (1988) reported that there was no relationship found between behavior change, including reported bleach use, and seroprevalence. In contrast, Watters (1994) reported that, although the seroprevalence rate among heterosexual injection drug users in San Francisco nearly doubled between 1986 and 1987, there was a stabilization of seroprevalence following the introduction of the bleach distribution and other HIV prevention programs. However, seroprevalent infections for which the date of onset of infection is unknown are not the optimal endpoint from which to measure effectiveness of an intervention, since other risk reduction factors, such as decreased needle sharing, were operating simultaneously. In such circumstances, any change in seroprevalence cannot be attributed solely to the bleach distribution programs.

More recently, Vlahov and colleagues have studied the relationship between the reported injection equipment disinfection practices of injection drug users and rates of HIV seroconversion. Their initial report (Vlahov et al., 1991) described a small nested case-control study of HIV seroconverters and HIV-seronegative injection drug users by their self-report frequency of using disinfectants all the time, less than all the time, and no use of disinfectants. Although no statistically significant protective effect was detected, the results of this study suggested a possible modest protective effect of bleach or alcohol disinfection among injection drug users who reported



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