1. Modeling the impact of the Mexican drug law reform on HIV incidence among people who inject drugs (PWID) in Tijuana, Mexico.
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Annick Bórquez, Leo Beletsky, Daniela Abramovitz, Steffanie A. Strathdee, Claudia Rafful, Peter Vickerman, MC Boily, Natasha K Martin
Division of Global Public Health, UCSD
Lisbon Addictions, 10/24/2017

2. Conflict of interest
None to declare

3. Drug law reform: Mexico
“Reforma de Narcomenudeo” depenalizes possession of a selection of drugs for personal consumption1,2 => decrease incarceration rates and police harassment and mandates drug treatment at 3rd apprehension => increase treatment rates
To be enforced from 2012 but so far, no substantial changes observed.1,2 Limited enforcement could generate a misleading message regarding the effectiveness of reform
Crucial to produce scientific evidence of its potential impact
1. Mackey TK et al. Mexico's "ley de narcomenudeo" drug policy reform and the international drug control regime. Harm reduction journal 2014; 11(1): 31.
2. Werb D. et al. Mexico’s drug policy reform: cutting edge success or crisis in the making? International Journal of Drug Policy 2014;.
Availability of concrete outcomes can serve as a motivation to policy makers and promote accountability.
Size of prison population over time in mexico and proportion incarcerated due to drug offences

4. Tijuana, as case study
Major transit route where drugs trafficked into US
Large PWID population (5, ,000)
Among PWID, HIV prevalence is 3.5%, HIV incidence is 1-2%/year
“Proyecto El Cuete IV”: cohort study following 734 PWID in Tijuana bi- annually from
HIV test
self-reports of sexual and drug- using behaviors, policing, incarceration, and access to harm reduction
following 734 PWID in Tijuana bi-annually from
HIV test
self-reports of sexual and drug-using behaviors, policing, incarceration, and access to harm reduction

5. Exposures among PWID in Tijuana
Incarceration
85% and 59% of male and female PWID have ever been incarcerated 5 (SD: 4.6) and 3 (SD: 2.7) times on average since starting injecting, respectively
80% of incarcerations approx. associated with drug use
=> No changes observed since 2011
Syringe confiscation by the police in past 6 months
11% reported having syringes confiscated by the police at baseline
=> Declined to 0% from 2011 to 2015
Drug treatment
Non evidence-based treatment (religious, 12 steps, mutual help)
Very limited access to opioid agonist therapy (OAT)

6. Aims Use mathematical modeling to:
1) Estimate the contribution of incarceration and police harassment to the HIV epidemic among PWID assuming no drug law reform from ;
2) Predict the potential impact of the Narcomenudeo reform under different enforcement scenarios from

7. Methods
Log-binomial regression to measure the relative risk of receptive syringe sharing associated with exposures of interest, controlling for duration of injection, using data at baseline ( )
Dynamic, deterministic compartmental model of HIV transmission among PWID
Injecting and sexual transmission
Varied parameters associated with demography, incarceration/syringe confiscation patterns and HIV transmission
Fitted to data on HIV prevalence and incidence using Latin Hypercube Sampling and resampled best fitting simulations
Disaggregated by sex, incarceration stage, syringe confiscation exposure, drug treatment and HIV stage

8. Model diagram
On OAT or
*In prison, no syringe confiscation by the police occurs as there is no interaction with the police. In the red square, involuntary treatment or opiate agonist therapy (OAT) instead of incarceration as alternative scenarios of the drug law reform implementation

9. Any receptive needle sharing
Relative risk of receptive syringe sharing by type of exposure among PWID in Tijuana
Any receptive needle sharing
Past 6 months
Relative risk
95%CI
p-value
Incarceration
Recent vs. None
1.40
1.21
1.63
<0.0001
Not recent vs. None
1.11
0.99
1.26
0.07
Syringe confiscation
Recent vs. Not
1.16
1.03
1.29
0.01
Involuntary treatment
Ever vs. Never
1.14
1.00
1.30
0.04

10. Modeling Analysis: Never incarcerated Prison
Baseline
Never incarcerated
Prison
Recently incarcerated (< 6 months ago)
Previously Incarcerated (> 6months ago)
Number of new HIV infections
Reproduce observed trends
Simplified cohort model used to estimate:
-Proportion ever incarcerated when starting injecting
-Primary incarceration rate
RR HIV
RR HIV

11. Contribution of incarceration and syringe confiscation to HIV incidence among PWID 2012-2030
Mean: 25.3%
Mean: 22.8%
Mean: 16.1%
Mean: 7.9%
Mean: 4.3%
Between 2012 and 2017, observed decline in syringe confiscation by the police resulted in a 2% (95% CrI: 0.3%-3%)reduction in the number of new HIV infections

12. Proportion of new infections averted under different Narcomenudeo reform enforcement scenarios

13. Conclusions
Incarceration contributes substantially to HIV incidence among PWID in Tijuana (PAF=23% between ).
 Missed opportunity of drug law reform to prevent infections
Reducing syringe confiscation and incarceration rates among PWID would have an impact on the epidemic
 Not sufficient to curb it
Involuntary treatment in non-evidence based centers would potentially increase HIV incidence among PWID
 If improperly implemented this public health oriented reform could have negative health consequences for PWID
Referral to evidence based drug treatment as mandated in the Narcomenudeo reform would potentiate the epidemic decline (20% reduction in incidence) among other positive outcomes.
 Need to scale up of OAT services in Tijuana

14. Acknowledgments Thank you! Funding:
-NIDA U.S.-Mexico drug abuse prevention research fellowship
-UC-MEXUS CONACyT postdoctoral fellowship
-UC San Diego Center for AIDS Research (NIAID P30 AI36214)
-NIDA grant R01 DA
-NIDA grant R01 DA A1
Patty González Zúñiga
Kenya Lazos
All the participants of El Cuete study
Thank you!
Pictures from “Tomorrow is a long time: Tijuana’s unchecked
HIV/AIDS epidemic” by John Cohen and Malcom Linton

15. Extra slides

16. Limitations and future work
Self reported behaviors
Need to establish causality
Model’s capacity to reproduce epidemic dynamics
Future work should examine:
Cost-effectiveness
Bayesian
sensitivity

18. Model fitting: