Estimating the size of crack cocaine users in France: Methods for an elusive population with high heterogeneity

BACKGROUND

Despite several sources corroborating an expanding market and increased visibility and greater diversity in users' profiles, very little is known about the number of crack cocaine users in France.

METHOD

The estimates rely on a single data source capture-recapture method. Annual data are extracted from treatment centres nationwide. To account for heterogeneity, we use an innovative zero-truncated geometric, regression-based estimator controlling for individual and centre characteristics. We use the well-known Zelterman estimator as a benchmark.

RESULTS

The number of crack cocaine users received in treatment centres increased dramatically, from 3388 in 2010 to 5143 in 2017 (+52%). The estimated number of crack cocaine users is believed to have tripled over the course of the same period (from 9775, 95% CI [8288-11530] to 28983 [24876-33766], respectively), with prevalences below 1‰, similar to other European countries. The coverage rate (observed number/estimated number of users) decreased in a similar fashion, indicating lower utilization. In particular, females and younger users are underestimated by data from treatment centres.

CONCLUSION

The prevalence of crack cocaine use is fairly low but steadily increasing. The diversity in users' profiles is a challenge to prevention and public health policies that should expand their scope to a more inclusive perspective of what defines crack cocaine users. Our method overcomes several methodological issues (data sources, data linkage, heterogeneity) and can be easily applied to a wide range of settings.

Revealing geographical and population heterogeneity in HIV incidence, undiagnosed HIV prevalence and time to diagnosis to improve prevention and care: estimates for France

Introduction

To close gaps in HIV prevention and care, knowledge about locations and populations most affected by HIV is essential. Here, we provide subnational and sub‐population estimates of three key HIV epidemiological indicators, which have been unavailable for most settings.

Methods

We used surveillance data on newly diagnosed HIV cases from 2004 to 2014 and back‐calculation modelling to estimate in France, at national and subnational levels, by exposure group and country of birth: the numbers of new HIV infections, the times to diagnosis, the numbers of undiagnosed HIV infections. The denominators used for rate calculations at national and subnational levels were based on population size (aged 18 to 64) estimates produced by the French National Institute of Statistics and Economic Studies and the latest national surveys on sexual behaviour and drug use.

Results

We estimated that, in 2014, national HIV incidence was 0.17‰ (95% confidence intervals (CI): 0.16 to 0.18) or 6607 (95% CI: 6057 to 7196) adults, undiagnosed HIV prevalence was 0.64‰ (95% CI: 0.57 to 0.70) or 24,197 (95% CI: 22,296 to 25,944) adults and median time to diagnosis over the 2011 to 2014 period was 3.3 years (interquartile range: 1.2 to 5.7). Three mainland regions, including the Paris region, out of the 27 French regions accounted for 56% of the total number of new and undiagnosed infections. Incidence and undiagnosed prevalence rates were 2‐ to 10‐fold higher than the national rates in three overseas regions and in the Paris region (p‐values < 0.001). Rates of incidence and undiagnosed prevalence were higher than the national rates for the following populations (p‐values < 0.001): born‐abroad men who have sex with men (MSM) (respectively, 108‐ and 78‐fold), French‐born MSM (62‐ and 44‐fold), born‐abroad persons who inject drugs (14‐ and 18‐fold), sub‐Saharan African‐born heterosexuals (women 15‐ and 15‐fold, men 11‐ and 13‐fold). Importantly, affected populations varied from one region to another, and in regions apparently less impacted by HIV, some populations could be as impacted as those living in most impacted regions.

Conclusions

In France, some regions and populations have been most impacted by HIV. Subnational and sub‐population estimates of key indicators are not only essential to adapt, design implement and evaluate tailored HIV interventions in France, but also elsewhere where similar heterogeneity is likely to exist.

Age of Initiation and Patterns of Use among People Who Inject Drugs Welcomed in Harm Reduction Facilities in France from 2006 to 2015

This exploratory analysis of time-series cross-sectional data provides insights on trends in age at first injection among people who inject drugs in France, and on associations with recent risky injecting behaviors. Data were collected from a national survey conducted in harm reduction facilities in five phases between 2006 and 2015. Standardized questionnaires collected information on demographics, substance use, and route of administration, as well as lifetime and past-month injection. Descriptive and multilevel models were applied to account for the hierarchical structure of the data. Prevalence of lifetime and past-month injection remained stable over time, while the prevalence of daily injection increased significantly. Mean age at first injection only appeared to increase for data collected after 2010. Gender differences in mean age at first injection decreased over time, suggesting the development of converging patterns of initiation independent of sex. After controlling for covariates, early initiation of injection was unrelated to daily injection or material sharing, and associated with the number of recently injected substances. Early initiation is likely a predictor of injected polysubstance use. Findings are relevant to the planning, implementation, and evaluation of prevention programs.