Declining prevalence of injection as main route of administration among heroin users treated in Spain, 1991-1993

The objetive of this study was to analyse the temporal and geographic trends and the factors associated with the prevalence of heroin injection (HI) in persons treated for the first time for heroin abuse/dependence in Spain in 1991-1993. The prevalence of HI was studied in 54,132 admissions to treatment reported to the State Information System on Drug Abuse, The factors associated with HI prevalence were studied by stratified analysis and logistic regression, Regions with similar prevalences were grouped together based on correspondence analysis, The HI prevalence declined progressively by year (50% in 1991, 43% in 1992 and 38% in 1993), The regions were grouped into 3 geographic areas, with rising prevalences in the southwest-northeast, Region was the factor most strongly asociated with HI, with an OR of 6.17 in the high prevalence group as compared with the low prevalence group, A declining trend of HI was seen with the more recent year of first use (OR of 0.15 for those beginning use in the years 1991-1993 as compared with those who began before 1982), later age at first use and increasing years of use, Male sex and cocaine use were associated with higher HI, Chasing is progressively replacing injection as a route of heroin administration because new users primarily use this route and probably because the most common transition is from injecting to chasing, The impact of the HIV epidemic and control programmes does not sufficiently explain this phenomenon. The main explanatory factors could be regional differences in the subculture of drug use or in the heroin market.