Decline in incidence of HIV and Hepatitis C virus infection among injecting drug users in Amsterdam; evidence for harm reduction? 1. Julius Center, University Medical Centre Utrecht, Utrecht, The Netherlands. 2. Public Health Service, Amsterdam, the Netherlands 3. Academic Medical Center, University of Amsterdam (CINIMA), Amsterdam, the Netherlands 4. Centre for Infectious Disease Control, RIVM, Bilthoven, The Netherlands. Anneke de Vos 1, Jannie van der Helm 2, Amy Matser 2, Maria Prins 2,3, Mirjam Kretzschmar 1,4

Cohort studies since 1985 (ACS) HIV & HCV: very strong incidence decline HIV: strong prevalence decline – introduction ~ 1980, peak ~ 1990 Harm reduction from 1981 – opiate substitution (methadone) – needle exchange facilities Amsterdam IDU

Changing demography – fewer new injectors → aging population Natural epidemic progression: – incidence ↔ prevalence – HIV-mortality ↔ population structure Amsterdam IDU Matser et al. 2012

Can we explain disease time-trends by demographic dynamics, assuming no effects of harm reduction? Method: individual based simulation modeling Study description

Injecting status – constant stop- and relapse-rates ACS participation status – recruitment of current injectors HIV & HCV status Mortality-rate by: – age – time since HIV infection – HIV treatment (from 1997) Risk behavior: high or low No harm reduction Modeled individuals Start injecting HCV+ Relapse injecting Stop injecting Recruitment ACS Death Stop injecting Low risk

Results

Decline in HIV & HCV incidence – fewer ever-IDU still injecting fits ACS data due to a constant stop-rate + fewer new IDU – high-risk infected sooner → low-risk left at risk HIV prevalence decline – high-risk IDU die faster → lowered population risk Results explained

cART introduction more gradual – better fit HIV prevalence decline Harm reduction; risk decline by calendar-time – can explain slight HCV prevalence decline – similar results for risk decline with age! – strong effects on risk consistent but not necessary Introduction of cART Results improved? Lowered risk?

Main trends in HIV and HCV among Amsterdam IDU could be explained by demographic changes Effects of harm reduction could not be disentangled from other causes Studies on the effects of harm reduction intervention should consider natural epidemic progression and demographics Summary & conclusion