injection drug users is particularly hazardous because it provides an efficient means for transmission of a number of blood-borne infectious diseases, including the HIV, hepatitis B (HBV), and hepatitis C viruses and the human T-cell leukemia viruses (HTLV-I and HTLV-II).

With the advent of the AIDS epidemic, the recognition of the rapid dissemination of HIV infection within injection drug user communities, and legal constraints associated with access to injection equipment (see Chapter 5), the use of bleach to clean and disinfect previously used needles and syringes has been encouraged by outreach workers in an attempt to improve the safety of the inherently unsafe practice of sharing needles and syringes among injection drug users. This chapter reviews the scientific literature on the efficacy of bleach as a disinfectant and the effectiveness of bleach distribution programs on reducing the potential harmful effects associated with injection drug use—risk behaviors and HIV transmission.

TRANSMISSION OF HIV AMONG INJECTION DRUG USERS

HIV is clearly a blood-borne pathogen. However, it is not yet known what proportion of HIV transmission between individuals results from the transfer of free infectious virus present in the plasma fraction of the blood of an infected individual, in the HIV-infected peripheral blood cells, or both. The sharing of needles and syringes by injection drug users can result in the transmission of pathogens spread as free virus (such as HBV) or via the transfer of infected cells (such as HTLV-I and HTLV-II). Resolution of the vehicle for HIV transmission may prove to be important, since HIV present within infected cells or as free virus may be differentially susceptible to the various available disinfection methods.

The actual amount (infectious dose) of HIV necessary to transfer the infection from one person to another is not known. In the absence of this information, attempts to model the effectiveness of any virus disinfection strategy are difficult because the level of inactivation needed to prevent transfer of the infection is unclear. Ideally, a disinfectant strategy will completely eliminate the infectivity of all HIV contaminating a surface. However, to be effective at limiting the transmission of HIV between individuals, such a strategy need only reduce the level of infectivity below the minimal infectious dose.

At present, the process of evaluating the effectiveness of various disinfection strategies relies on tissue culture models, in which virus inactivation is measured by the ability to isolate infectious virus following disinfectant treatment. Unfortunately, it is not known whether the available tissue culture-based HIV isolation methods are sensitive enough to detect the minimum infectious dose of virus responsible for transferring HIV infection between individuals. If virus isolation methods are not sensitive enough, a



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