Estimating the size of the HIV epidemic among injecting drug users in Amsterdam

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

AIMS

In Amsterdam, HIV prevalence has nearly halved among injecting drug users (IDU) since 1990. Hepatitis C virus (HCV) prevalence also declined; HIV and HCV incidence dropped to nearly zero. We examined possible explanations for these time trends, among which the implementation of harm reduction measures aimed at reducing the risk behaviour of IDU.

DESIGN

We used individual-based modelling of the spread of HIV and HCV. 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. We considered different scenarios of risk behaviour.

SETTING

IDU in Amsterdam.

MEASUREMENTS

Simulated HIV and HCV incidence and prevalence were compared with ACS data.

FINDINGS

Assuming that harm reduction measures had led to a strong decrease in risk behaviour over time improved the model fit (squared residuals decreased by 30%). However, substantial incidence and HIV prevalence decline were already reproduced by incorporating demographic changes into 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.

CONCLUSIONS

Marked decreases in HIV and HCV in Amsterdam since 1990 could be due partly to harm reduction measures; however, they may also be attributable largely 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.

Trends in HIV seroprevalence among patients with sexually transmitted diseases in 17 European sentinel networks, 1990-1996. European Study Group

OBJECTIVE

To monitor trends in HIV seroprevalence among sentinel populations of patients with new sexually transmitted disease episodes in 17 networks of 15 European countries.

METHODS

Time trends were estimated by logistic regression for homo-/bisexual men, injecting drug users (IDU) and non-IDU heterosexuals. The networks were included as independent variables to account for different prevalence levels across Europe. Socio-demographic and behavioural data were also included in the model. The interactions of time and each factor in the model were evaluated to determine whether trends differed across networks or population subgroups.

RESULTS

Overall, more than 150,000 sexually transmitted disease episodes were registered in this study. In the European network as a whole, the prevalence decreased significantly among IDU [n = 2619; odds ratio (OR) for annual change, 0.86; 95% confidence interval (CI), 0.80-0.93]. It also decreased among homo-/bisexual men (n = 11,809; OR, 0.92; 95% CI, 0.89-0.94). In both groups, trends did not differ statistically between networks. Among non-IDU heterosexuals (n = 114,024) the prevalence increased significantly (OR, 1.08; 95% CI, 1.04-1.13), especially among women (OR, 1.13) and the time trends differed statistically across networks. A significant increase was observed in four networks, whereas no specific change was detected in the others.

CONCLUSIONS

By applying a standardized protocol, trends in HIV prevalence could be compared across networks and estimated at a more global level. For the validity of HIV trends in such surveys, it is essential to minimize the number of patients not being tested in networks where voluntary testing is required.