nonprescription needles, which suggests a high level of motivation on the part of cohort members to avoid HIV infection.

Therefore, in light of these findings, it would be misleading to consider the outreach efforts undertaken solely as bleach distribution programs.

Limitations of Bleach Disinfection

Although bleach, when properly used, provides an effective disinfectant in the health care setting, a number of variables may limit its effectiveness when used by injection drug users to disinfect contaminated needles and syringes. The physical and biological parameters that govern the effectiveness of any disinfectant (discussed earlier in this chapter) are critically important factors in determining whether the cleaning and disinfectant method used by a given injection drug user will result in effective disinfection of their injection equipment. Needles and syringes are not designed for reuse and are difficult to completely clean and disinfect. The presence of organic matter in the residual blood, either liquid or dried, remaining in the contaminated injection equipment decreases the potency of bleach as a disinfectant. The presence of blood in a previously used syringe necessitates thorough rinsing with water prior to bleach treatment. Residual, potentially infectious HIV present within clotted blood may be even more resistant to elimination by cleaning and disinfection methods. Furthermore, the infectivity of HIV-infected cells found within the blood remaining in used needles and syringes may be more resistant to disinfection than the cell-free or cell-associated HIV preparations studied in laboratory settings.

Reports by Shapshak and colleagues (Shapshak et al., 1993, 1994; McCoy et al., 1994) indicate that complete inactivation of preparations of cell-free HIV that had been concentrated (''pelleted") by centrifugation required prolonged (greater than 30 second) exposure to undiluted bleach. Although the laboratory model used in this study does not directly approximate the real-life circumstances of bleach disinfection of contaminated injection equipment, these reports resulted in significant concern and confusion about the validity of previous recommendations concerning bleach disinfection methods.

Another factor that may limit the effectiveness of disinfection efforts is that needles and syringes may become recontaminated if other drug injection paraphernalia, such as the cooker or the cotton used, are not cleaned or replaced (Koester et al., 1990). However, two studies (Marmor et al., 1987; Samuels et al., 1991) have found no association between shared cookers and HIV seroprevalence. Sharing water for mixing drugs or for rinsing the syringe after bleach use is another source of contamination (Koester et al., 1990; Inciardi and Page, 1991). Various methods of dividing drugs for sharing purposes also hold the potential for contamination (see Chapter 1).

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