Identifying heterogeneity among injection drug users: a cluster analysis approach.

OBJECTIVES: We used cluster analysis to subdivide a population of injection drug users and identify previously unknown behavioral heterogeneity within that population. METHODS: We applied cluster analysis techniques to data collected in a cross-sectional survey of injection drug users in Winnipeg, Manitoba. The clustering variables we used were based on receptive syringe sharing, ethnicity, and types of drugs injected. RESULTS: Seven clusters were identified for both male and female injection drug users. Some relationships previously revealed in our study setting, such as the known relationship between Talwin (pentazocine) and Ritalin (methylphenidate) use, injection in hotels, and hepatitis C virus prevalence, were confirmed through our cluster analysis approach. Also, relationships between drug use and infection risk not previously observed in our study setting were identified, an example being a cluster of female crystal methamphetamine users who exhibited high-risk behaviors but an absence or low prevalence of blood-borne pathogens. CONCLUSIONS: Cluster analysis was useful in both confirming relationships previously identified and identifying new ones relevant to public health research and interventions.