[The prevalence of human immunodeficiency virus infection and the risk behaviors in the heroin addicts of Barcelona, Madrid and Seville: an example of the advantages of centering studies on addicts and not just on intravenous users]. 
The switch from intravenous heroin administration to smoking of heroin might be changed the trends in the prevalence of HIV infection and risk behaviours among Spanish users.  Cross-sectional study of 909 regular heroin users, recruited within and outside of drug treatment centres.  The prevalence of HIV infection and risk behaviours were studied in the whole sample and among injectors.  The proportion of heroin users who had ever injected was 86.7% in Barcelona, 71.1% in Madrid and 56.1% in Seville, while the proportion of those who had injected in the last 30 days was 79.7, 35.6 and 29.2%, respectively.  The prevalence of HIV infection among users who had ever injected was 46.2% in Barcelona, 39.6% in Madrid and 47.1% in Seville; in the total population of heroin users the prevalence was 40, 31.1 and 28%, respectively.  Among current injectors, 10.9% in Barcelona, 13.9% in Madrid and 23.6% in Seville reported they had injected with used syringes in the last 30 days, while the corresponding proportion among the total population of users was 8.7, 4.9 and 6.9%, respectively.  Moreover, 19.2% of injectors in Barcelona, 16.7% in Madrid and 16.9% in Seville admitted to injecting drugs which had been diluted in syringes previously used by others in the last 30 days; of this group, over half stated they had not injected with used syringes during that period.  The prevalence of HIV infection and risk behaviours among heroin users differs depending on whether all users or only injectors are considered.  This suggests that the transition from injecting to smoking is one of the major factors contributing to the control of the HIV epidemic in Spain.  This contribution, which has little to do with regional prevention policies, must be taken into account when comparing their effectiveness.