Temporal trends in injection drug use among Black and White adult residents of US metropolitan areas (1992-2002)

Background: No data exist documenting temporal and spatial trends in injection drug use (IDU) within racial/ethnic groups. We present a method of estimating IDU prevalence among Black and White residents of 95 large US metropolitan statistical areas (MSAs) over time (1992-2002) and describe resulting trajectories. Methods: We estimated the number of Black adult IDUs in each MSA and year by multiplying the proportion of IDUs who were Black (estimated by analyzing databases documenting IDUs' encounters with three healthcare systems) by the total number of IDUs in each MSA and year (calculated using multiplier/allocation methods). For each MSA and year, the number of Black IDUs was divided by the number of Black adults. We calculated White IDU prevalence using identical procedures. Prevalence trajectories were described using hierarchical linear models. Results: IDU prevalence declined initially in both racial/ethnic groups, but declines were only partially sustained. Though the mean IDU prevalence was higher for Black adults than White adults in 1992 (281 IDUs/10,000 adults vs. 110 IDUs/10,000 adults), the initial rate of decline was greater for Blacks than Whites (-6.24 vs. –1.89 IDUs/10,000 adults) and Black IDU prevalence began to rise later in the study period than White IDU prevalence (2000 vs. 1998). Discussion: The determinants of these trajectories merit investigation, and may include mounting AIDS-related deaths among injectors in the early-to-mid-1990s (borne disproportionately by Black injectors); reduced likelihood of initiating IDU (also reported disproportionately by Black drug users); and transitions to other modes of drug use (or to abstinence) among active injectors.