Injecting drug users (IDUs) are vulnerable to a wide range of viral and bacterial infections through poor injection hygiene. These infections, which include HIV, hepatitis C and hepatitis B, result in considerable levels of morbidity and mortality. With an estimated 750,000 to 1 million active IDUs in the European Union (EU), these infections have the potential to place a considerable burden on European healthcare systems, as well as adversely impacting on the well-being of those who inject drugs.

Interventions have been adopted throughout Europe that aim to reduce risk of these infections; these interventions include opiate substitution therapy (OST) and needle and syringe exchange programmes (NSPs), both of which have been shown to effective in preventing infections. They aim to reduce infections by changing the behaviours that place individuals at risk of infection, such as through reducing the sharing and reuse of injecting equipment and by decreasing the frequency of drug injection. Monitoring the levels of these behaviours is thus important for assessing the impact of intervention programmes. The systematic collection of information on risk and protective behaviours is therefore an important part of second-generation HIV surveillance systems. Behavioural surveillance focused on IDUs often looks at behaviours related to a range of viral infections of the blood, not just HIV, due to the similarities in the routes of transmission.