Continuing injecting risk behaviour: results from the Amsterdam Cohort Study of drug users

To give a detailed description of injection-related risk behaviours, and to estimate the relative importance of these behaviours with regard to HIV transmission.

The present study was part of the Amsterdam Cohort Study of drug users.

In Amsterdam, a city with extensive preventive measures, large HIV-risk reductions have taken place, but no further decreases have occurred since 1991.

A detailed questionnaire on injecting risk behaviour was completed by a cross-section of participants in 1992/93 (n = 168). Among 48 HIV-seroconverters, a questionnaire was completed concerning possible HIV-transmission route.

Of 96 HIV-negative participants, 23% deliberately borrowed a used syringe, 18% reported possible "accidental" borrowing, 9% front/backloading, 4% simultaneous injection, and 32% possible sharing of ancillary equipment. Of deliberate borrowers, 64% borrowed from a person with unknown or positive HIV serostatus, and 81% did not appropriately clean the equipment; 79% borrowed in the absence of serious withdrawal symptoms. Risk factors differed for deliberate and 'accidental' borrowing. Among the HIV seroconverters, the most likely transmission route was borrowing in 29% of cases, front/backloading in 8%, borrowing or front/backloading in 21%, unprotected sexual contact in 23% (mainly with regular partner) and either injecting or sexual risk in 13%. Women were much more likely to report sexual transmission (p = 0.016). Borrowing was admitted by 43% before, and 64% after awareness of HIV-seroconverion.

As the injecting risk is high, usually deliberate, and often in the absence of withdrawal symptoms, further prevention seems difficult. Although deliberate borrowing is the main risk for HIV seroconversion, unprotected sexual contacts and front- and backloading may be more important than previously thought in Amsterdam. Under-reporting of borrowing is probably substantial, but does not alter the above conclusions.