interesting to note that, by focusing on active injectors not in treatment, this program exclusively enrolled members of the hard-core drug-using population, which the major household and student surveys underrepresent. Nevertheless, the fact that the mean age of subjects in the 28-site NADR analysis ranged from ages 31 to 40 and the mean years of injection drug use ranged from 10 to 19 suggests that this database overrepresents the most long-standing and active subpopulation of hard-core injection drug users. As a consequence, it appears that NADR was more successful in recruiting well-established social networks of injection drug users than recent initiates or occasional users. Despite these limitations, the NADR study is important because it shows that a large proportion of injection drug users had no history of drug abuse treatment, despite mean duration of injection of 10 to 19 years. This suggests that there is a subgroup of injection drug users not being accessed into treatment. However, a substantial proportion of these high-risk injection drug users do have a repeated history of treatment, suggesting that treatment as an HIV prevention activity may need to be supplemented (Siegal, 1995).

Additional studies suggest that there may be a secular trend toward reductions in high-risk injection practices. Several studies have reported decreases in risk over time (Battjes et al., 1992; Selwyn et al., 1987; Celentano et al., 1991). For example, Vlahov et al. (1991c) studied an out-of-treatment sample of injection drug users in Baltimore. They focused on behaviors during the 3 months following injection incidence, examining time trends from 1982 through 1987 among successive cohorts of injection drug users classified according to the year in which they first injected. They found significant increases over time in the proportion who sometimes used sterile needles, a decrease in the proportion always using equipment that had previously been used by others, and a decrease in the number of needle-sharing partners. Another relevant finding was a dramatic shift in the first drug injected from heroin to cocaine between 1982 and 1987.

Local Drug Use Trends and Patterns

As succeeding chapters of this report will make clear, a critical aspect of drug use is that it is specific to regions and communities. Although its reports do not focus upon injection drug use alone, the proceedings of NIDA's Community Epidemiology Work Group (CEWG) further illustrate the diversity of injection drug-using patterns across the country and the extent to which these patterns change over time. The CEWG is a drug abuse surveillance network composed of researchers from 20 major U.S. metropolitan areas: Atlanta, Boston, Chicago, Dallas, Denver, Detroit, Honolulu, Los Angeles, Miami, Minneapolis, Newark, New Orleans, New York, Philadelphia, Phoenix, St. Louis, San Diego, San Francisco, Seattle, and



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