The formulated objectives of the study were:
1 to measure and compare patterns of high-risk behaviour in relation to HIV seroprevalence in EC and COST countries using a common methodology;
2 to measure the change in behaviour and prevalence over a period of time, in relation to preventive measures.
The import role played by injecting drug users (IDU) in the epidemic of HIV infection is well known. In certain countries in Europe, most notably Spain and Italy, they account for the majority of AIDS cases, following a rapid spread of infection within the IDU community. It has often been stated that IDU may play an important role in the feared heterosexual HIV epidemic, through sexual contact with people who do not belong to any of the established high-risk groups, particularly if IDU turn to prostitution to support their drug habit. Because of this situation, many resources and much effort go into providing services aimed at promoting behaviour carrying no - or at least reduced - risk of transmitting HIV. Examples range from the simple distribution of information at points of contact with IDU to the provision of needle exchanges, operating either as relatively isolated projects or as part of large-scale 'harm reduction' programmes.
It is important to try to understand the factors associated with high-risk behaviour (unsafe injecting and unsafe sexual behaviour), which appears to persist at a high level despite preventive measures. It is also important to see how these factors vary between areas. There are major geographical variations in HIV prevalence among IDU, even in adjacent cities. Against this background, a proposal was made for an EC Concerted Action which would have as its principal objective the collection of data in order to permit a comparison of associated patterns across countries. Furthermore, since so much investment has been made in promoting behavioural change, a second aim was to discover to what extent change in the relevant criteria was in fact taking place.