Harm reduction among drug users dramatically reduces new HIV and Hepatitis C virus infections

Decline in incidence of HIV and Hepatitis C virus infection among injecting drug users in Amsterdam; evidence for harm reduction?

de Vos AS, van der Helm JJ, Matser A, Prins M, Kretzschmar ME. Addiction. 2013 Jan 24. doi: 10.1111/add.12125. [Epub ahead of print]

In Amsterdam HIV prevalence has nearly halved among injecting drug users since 1990. Hepatitis C Virus (HCV) prevalence also declined, HIV and HCV incidence dropped to nearly zero. The authors examined possible explanations for these time trends, among which the implementation of harm reduction measures aimed at reducing risk behavior of IDU. Individual-based modeling of the spread of HIV and HCV was used. Information about demographic parameters was obtained from the Amsterdam Cohort Study (ACS) among drug users. The model included changes in inflow of new IDU and death-rates over time, the latter dependent on age and time since HIV-seroconversion. Different scenarios of risk behavior were considered. Simulated HIV and HCV incidence and prevalence were compared with ACS data. Assuming harm reduction measures had led to strong decrease in risk-behavior over time improved the model fit (squared residuals decreased by 30%). Substantial incidence and HIV prevalence decline were reproduced by incorporating demographic changes in the model. In particular, lowered disease spread might be a result of depletion of high-risk IDU among those at risk for disease, and a decrease in the number of high-risk individuals in the population due to HIV-related mortality. Marked decreases in HIV and HCV in Amsterdam since 1990 could be partly due to harm reduction measures; however, they may also be largely attributable to changes in the IDU population. Future research aimed at quantifying the benefits of interventions should not neglect the impact of natural epidemic progression and demographic changes.

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Editor’s notes: This article from Amsterdam highlights the impressive information that HIV and HCV incidence has dropped nearly to zero among drug users. Modeling exercises indicate that it is a challenge to attribute the cause of these results, however clearly harm reduction measures have been widely implemented, beyond the level seen in many other countries where drug users are a key population at risk for HIV acquisition.

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