The purpose of the analysis described here was to classify not-in-treatment drug users participating in the National Institute on Drug Abuse (NIDA) - sponsored Cooperative Agreement study into several « homogeneous » HIV risk groups using cluster analysis.

Data for this analysis (N=17,778) were collected at 19 study sites in the United States and Puerto Rico.

Measures selected for the cluster analysis were limited to (a) current drug use and HIV risk behaviors, (b) mutually exclusive behaviors, (c) behaviors directly related to HIV risk, and (d) behaviors that were not statistically rare.

Eight homogeneous HIV risk clusters were produced.

Crack cocaine use was the most distinguishing feature of three clusters.

Another three clusters were distinguishable by drug injection and needle use practices.

Two additional clusters could not be grouped with either the crack-or the injection-dominant clusters.

Prostitution was the most distinguishing risk behavior of one of these clusters, and extremely high drug injection frequencies and relative rates of risky needle use characterized the other.

Composition of the clusters varied significantly by gender, race/ethnicity, educational attainment, and drug use characteristics.

In addition, perceptions and behaviors initiated to reduce the chances of becoming infected with HIV varied by cluster.

Subjects in the crack-predominant clusters reported low perceptions of the chances of getting AIDS. (...)