Decline in HIV Incidence and Injecting, But Not in Sexual Risk Behaviour, Seen in Drug Users in Amsterdam: a 19-Year Prospective Cohort Study

The researchers set out to examine temporal changes in HIV incidence, transmission routes, and sexual and injecting risk behavior in the open Amsterdam Cohort Study (ACS) among drug users. ACS, which was initiated in 1985, allows the study of changes in trends since 1996, when the use of highly active antiretroviral therapy (HAART) became widespread.

The team used person-time techniques to study the trend in HIV incidence among HIV-negative drug users. Subjects' answers to detailed standardized questionnaires provided information on HIV transmission routes. A logistic regression model, adjusted for correlations between visits of the same individual, was used to evaluate trends in injecting and sexual risk behaviors.

The study of 1,315 HIV-negative persons, of whom 93 became HIV-positive, yielded 6,970 HIV-negative person-years of follow-up. HIV incidence was seven per 100 person-years in 1986 and ranged from 0 to 0.5 per 100 person-years after 1999. The odds ratio was 15.6 (95 percent confidence interval, 2.6-94.6) for HIV transmission through unprotected heterosexual contact versus injecting after 1996 compared with the previous period. From 1985 to 2004, reports of both injecting and borrowing needles declined significantly. Reports of sexual risk behavior and STD infection at follow-up visits decreased before 1996 but not after 1996.

Since 1985, HIV incidence among ACS drug users has declined, the researchers reported. "Accompanied by a reduction in injecting drug use and needle sharing, this decline occurred despite continued sexual risk behaviour," the researchers concluded. "At present, new HIV seroconversions are related mainly to unprotected heterosexual contacts. Therefore, HIV prevention programmes for drug users should pay specific attention to the importance of safe sex practices."

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