two in Texas, two in the South, and the other in San Juan, Puerto Rico. Thus, it is clear that injection drug users are geographically dispersed throughout the nation, notwithstanding the density in the Northeast corridor.

Few national estimates of injection drug users as geographically specific as those provided by Holmberg have been published, making comparisons difficult; however, one estimate is that provided for New York City. In a paper commissioned by this panel, Frank and Williams (1994) review the history of narcotic use and prevalence estimation in New York. A narcotics registry was maintained in New York City from 1965 to 1974 in an attempt to approximate a census of addicts. During this period, almost 900,000 reports were recorded on nearly 300,000 individuals. More than 95 percent of the individuals reported were using heroin, which at the time was considered almost tantamount to being identified as an injector. Utilizing the registry as a foundation for the years 1970 to 1974 and then developing a synthetic estimation model to project for later years, Frank and Williams estimated the numbers of narcotic abusers in New York City to be 165,000 in 1970 and 200,000 in 1980. The authors suggest that the number of heroin injectors in New York City is now probably less than the 1980 figure of 200,000 due to AIDS mortality and the growing popularity of snorting heroin as a route of administration, but no more recent prevalence estimates have been attempted. The authors do not account for the possible shift in type of drug injected (i.e., cocaine), which might be missed by their methodology. Nonetheless, the Frank and Williams estimate is in accordance with Holmberg's New York City figure of 168,300.

National Surveys of Drug Abuse

Another source of information about the size of the injection drug use population is national surveys of substance abuse.

National Household Survey on Drug Abuse

The National Household Survey on Drug Abuse (NHSDA) of the Substance Abuse and Mental Health Services Administration (SAMHSA) provides an important source of data on drug use among the general population, although it cannot estimate the entirety of the injection drug user population in the country. In particular, it has major problems as a precise basis for estimating numbers of hard-core drug users, including injectors (National Institute on Drug Abuse, 1994a; U.S. General Accounting Office, 1993). The representative sample of households excludes injection drug users who are homeless, institutionalized, or transient, and the injection drug users who are approached may be reluctant to participate. Also, the



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