[Drug injection method risky for transmission of blood-borne diseases: are we careful enough?].

In the last 20 years, research on the determinants of the HIV epidemic among drug users has focused mainly on studies of risk behaviour for drug injection. Studies involving human behaviour present special methodological problems. This paper presents a review of 1) the most important features that make this field different from the study of blood-borne diseases in other populations, and 2) the basic variables used in epidemiology to analyse injecting risk behaviour. Alternatives to improve research planning and results are proposed based on collaborating with other disciplines and improving the methodological resources of epidemiology.