Environmental conditions, political economy, and rates of injection drug use in large US metropolitan areas 1992-2002.

City-specific studies have suggested the quality of the local environment and economic circumstances are associated with greater risk of injection drug use (IDU). No studies have assessed the relation among the quality of the local environment, economic circumstances, and IDU over time across US metropolitan areas. Annual numbers of IDUs in the 88 largest US metropolitan statistical areas (MSAs) were estimated by extrapolating, adjusting, and allocating existing estimates using various data sources. Generalized estimating equations were used to assess the relation among the quality of the local environment, metropolitan political economy, and IDU prevalence using lagged models taking into account potential confounders. MSAs with a worse local environment (measured as a one standard deviation difference) had a greater risk of IDU (relative risk [RR]=1.03, 95% confidence interval [CI]: 1.01, 1.06); similarly, a one-percentage point worsening of the political economy for an MSA was associated with greater risk of IDU (RR=1.04-1.10). Final models stratified by region indicated heterogeneity of effect by region whereby the quality of the local environment was associated with IDU strongest in the South (RR=1.12, CI: 1.05, 1.12) followed by the West (RR=1.04, CI: 1.01, 1.07) and Midwest (RR=1.03, CI: 1.00, 1.06), and the metropolitan political economy was associated with IDU in the West (RR=1.03-1.09) and Northeast (RR=1.04-1.12). Our results underscore the importance of sociopolitical factors as determinants of IDU in MSAs. Structural solutions targeted at improving environmental conditions and economic circumstances should be considered as drug use interventions.