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Modeling the contribution of incarceration to
HIV incidence among people who inject drugs
in Tijuana, Mexico
Annick Bórquez, Natasha K Martin, Daniela Abramovitz, Steffanie A Strathdee
Division of Global Public Health, University of California San Diego
In collaboration with: Leo Beletsky, Peter Vickerman, Patricia González-Zúñiga, Gudelia
Rangel, Matthew Hickman
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Drug law reform: Mexico
• Amendments to Single Convention on Narcotic Drugs being
implemented by countries as criminalization has not reduced
burden1,2.
• “Ley de Narcomenudeo” depenalizes possession of a selection of
drugs for personal consumption3,4. To be enforced from 2012 but
so far, no substantial changes observed3,4
• Limited enforcement could generate a misleading message
regarding the effectiveness of reform
 Crucial to produce scientific evidence of its missed impact
1. Moore L. and Elkavich A. Who’s using and who’s doing time. Incarceration, the war on drugs and public health. American Journal of
Public Health, May 2008, Vol 98, No. 5
2. Beyrer C, et al. Prisoners, prisons, and HIV: time for reform. The Lancet, July 14 2016
3. 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.
4. Werb D. et al. Mexico’s drug policy reform: cutting edge success or crisis in the making? International Journalof Drug Policy 2014;.
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Tijuana case study
• Major transit route where drugs
trafficked into US
• Among PWID, HIV prevalence is 3.5%,
HIV incidence is 1%
• “Proyecto El Cuete IV”: cohort study
following 734 PWID in Tijuana bi-annually from 2011-2020
• HIV test
• self-reports of sexual and drug-using behaviors, policing,
incarceration, and access to harm reduction
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Aims
• Describe incarceration patterns and associated
behaviors among PWID in Tijuana, Mexico
• Use mathematical modeling to:
– Estimate contribution of incarceration to the HIV
epidemic among PWID since start of drug reform to
date (2012-2016)
– Estimate potential impact of stopping incarceration
or HIV transmission in prison on cumulative
incidence among PWID from 2012 to 2016
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Methods
• Descriptive statistics of incarceration patterns
and binary logistic regression for HIV associated
behaviors using data at baseline (2011-2012)
• Dynamic, deterministic compartmental model of
HIV transmission among PWID
– Injecting and sexual transmission
– Disaggregated by sex, incarceration status, and HIV
stage
– Parameterized with data from the statistical analyses
and other epidemiological data in Tijuana
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Incarceration patterns and HIV
infection among PWID in Tijuana
– 85% and 59% of male and female PWID have ever been incarcerated
– Mean number of 5 (SD: 4.6) and 3 (SD: 2.7) incarcerations since
starting injecting for male and female PWID, respectively
1
Proportion ever incarcerated
0.8
0.6
0.4
0.2
0
0
10
20
30
40
Injecting duration
– Relative risk of HIV infection among ever incarcerated compared to
never incarcerated is 1.1 among males and 3.2 among females
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Effect of incarceration on HIV
associated risk behaviors
Incarceration
Any receptive needle
sharing
Needle sharing at least
half the time
Never using condoms
w/ casual partner
Recent vs. None
Not recent vs. None
Recent vs. None
Not recent vs. None
Recent vs. None
Not recent vs. None
Females
Males
Odds
Odds
95%CI
95%CI
Ratio
Ratio
6.4 0.8 -50.7 5.1
1.1 -24.3
1.6 0.9 -2.7
1.4
0.8 -2.4
5.7 1.6 -19.6 0.7
0.2 -2.1
1.8 1.1 -3.0
0.8
0.5 -1.4
0.7 0.1 -7.2
3.1
0.5 -17.2
2.2 1.1 -4.6
0.6
0.3 -1.3
Outputs used to inform relative
risk of infection among those incarcerated
in model
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Model parameterization and
calibration
• Varied parameters associated with
demography, incarceration patterns and HIV
transmission, including RR of infection by
incarceration stage
• Fitted to data on HIV prevalence and
incidence using Latin Hypercube Sampling
• 50,000 parameter sets and resampled runs
with Log-likelihood>99th percentile
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Number of new HIV infections
Analysis: PAF of incarceration to HIV incidence
RR HIV
RR HIV
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Baseline
2012
2016
Results: PAF of incarceration among
PWID in Tijuana 2012-2016
PAF of incarceration to HIV incidence
45%
IQR
95% CrI
35%
25%
15%
5%
-5%
Full effect
Risk at release Long term risk
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Female
Male
Potential intervention impact: 20122016
Proportion of new HIV infections
averted
25%
IQR
95% CrI
20%
15%
10%
5%
0%
Stop incarceration
-5%
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Stop transmission in prison
Conclusions
• Incarceration contributes substantially to HIV incidence
among PWID in Tijuana (PAF=25%), mostly due to longterm impact on risk.
Missed opportunity of drug reform to prevent infections
• Incarceration of female PWID contributes
disproportionately to incidence considering small
population size and lower incarceration rates
Need focus on this particularly stigmatized population
• While elimination of incarceration would have a small
impact in the short term, stopping transmission in
prison would be an efficient way to reduce incidence
Need scale-up of harm reduction interventions in prison
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Limitations and future work
• Self reported behaviors
• Interpretation of OR for the association of
incarceration with risk behaviors
• Model’s capacity to reproduce epidemic
dynamics
Future work should examine:
– the potential impact and feasibility of implementing
HIV interventions in Tijuana prisons
– Cost-effectiveness of the reform enforcement
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Acknowledgments
Kenya Lazos
Patty Gonzáles Zúñiga
Claudia Rafful
Mario Morales
All the participants of El Cuete
study
Funding:
-UC-MEXUS CONACyT postdoctoral
fellowship
-UC San Diego Center for AIDS Research
(NIAID P30 AI36214)
-NIDA U.S.-Mexico drug abuse
prevention research fellowship
-NIDA grant R01 DA0 19829
-NIDA grant R01 DA037773-01A1
-UCSD CFAR grant P30 AI036214
Pictures from “Tomorrow is a long time: Tijuana’s unchecked
#AIDS2016 | @AIDS_conference HIV/AIDS epidemic” by John Cohen and Malcom Linton
Tijuana Wound Clinic
SEP and basic medical
assistance to PWID
• Fundraising:
https://www.generosity.com/medicalfundraising/Tijuana-wound-clinic-fundraiser
Video: https://youtu.be/yUpsL_pJkU4
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Model: HIV transmission
• Dynamic HIV transmission
through receptive needle
sharing
• Proportionate mixing
• Simplified HIV-Syphilis coinfection model used to
estimate contribution of
sexual transmission: 2575%
Susceptible
Acute infection
Latent infection
Pre-AIDS
ART
AIDS
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PAF of incarceration 2012-2030
70%
60%
50%
40%
30%
20%
10%
0%
-10%
Full effect
-20%
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Risk at release
Long term risk
Potential intervention impact 20122030
35%
30%
25%
20%
15%
10%
5%
0%
Stop incarceration
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Stop tranmission in prison