Sex and drugs: cost-effectiveness of risk reduction programmes for female sex workers who inject drugs in Mexico

Cost-effectiveness of combined sexual and injection risk reduction interventions among female sex workers who inject drugs in two very distinct Mexican border cities.

Burgos JL, Patterson TL, Graff-Zivin JS, Kahn JG, Rangel MG, Lozada MR, Staines H, Strathdee SA. PLoS One. 2016 Feb 18;11(2):e0147719. doi: 10.1371/journal.pone.0147719. eCollection 2016.

Background: We evaluated the cost-effectiveness of combined single session brief behavioral intervention, either didactic or interactive (Mujer Mas Segura, MMS) to promote safer-sex and safer-injection practices among female sex workers who inject drugs (FSW-IDUs) in Tijuana (TJ) and Ciudad-Juarez (CJ) Mexico. Data for this analysis was obtained from a factorial RCT in 2008-2010 coinciding with expansion of needle exchange programs (NEP) in TJ, but not in CJ.

Methods: A Markov model was developed to estimate the incremental cost per quality adjusted life year gained (QALY) over a lifetime time frame among a hypothetical cohort of 1000 FSW-IDUs comparing a less intensive didactic vs. a more intensive interactive format of the MMS, separately for safer sex and safer injection combined behavioral interventions. The cost for antiretroviral therapy was not included in the model. We applied a societal perspective, a discount rate of 3% per year and currency adjusted to US$2014. A multivariate sensitivity analysis was performed. The combined and individual components of the MMS interactive behavioral intervention were compared with the didactic formats by calculating the incremental cost-effectiveness ratios (ICER), defined as incremental unit of cost per additional health benefit (e.g., HIV/STI cases averted, QALYs) compared to the next least costly strategy. Following guidelines from the World Health Organization, a combined strategy was considered highly cost-effective if the incremental cost per QALY gained fell below the gross domestic product per capita (GDP) in Mexico (equivalent to US$ 10 300).

Findings: For CJ, the mixed intervention approach of interactive safer sex/didactic safer injection had an incremental cost-effectiveness ratio (ICER) of US$4360 ($310-$7200) per QALY gained compared with a dually didactic strategy. Using the dually interactive strategy had an ICER of US$5874 ($310-$7200) compared with the mixed approach. For TJ, the combination of interactive safer sex/didactic safer injection had an ICER of US$5921 ($104-$9500) per QALY compared with dually didactic. Strategies using the interactive safe injection intervention were dominated due to lack of efficacy advantage. The multivariate sensitivity analysis showed a 95% certainty that in both CJ and TJ the ICER for the mixed approach (interactive safer sex didactic safer injection intervention) was less than the GDP per capita for Mexico. The dual interactive approach met this threshold consistently in CJ, but not in TJ.

Interpretation: In the absence of an expanded NEP in CJ, the combined-interactive formats of the MMS behavioral intervention is highly cost-effective. In contrast, in TJ where NEP expansion suggests that improved access to sterile syringes significantly reduced injection-related risks, the interactive safer-sex combined didactic safer-injection was highly cost-effective compared with the combined didactic versions of the safer-sex and safer-injection formats of the MMS, with no added benefit from the interactive safer-injection component.

Abstract [1]  Full-text [free] access  [2]

Editor’s notes: Female sex workers who inject drugs are a particularly vulnerable group with potential risks of HIV infection stemming from both condomless sex and use of contaminated injecting equipment. In the northern border towns of Mexico, which are on major drug trafficking routes into the United States, the prevalence of HIV among female sex workers who inject drugs is 12%. This is in comparison with 6% among female sex workers who do not inject drugs and 0.3% among the general population. In this context, the authors conducted a cost-effectiveness analysis of a combined single-session brief behavioural programme. It was either didactic or interactive, to promote safer sexual and injection practices among female sex workers who inject drugs in two Mexican cities: Ciudad Juarez and Tijuana.

The authors found that the programme can be highly cost-effective in reducing HIV risky behaviours, although with varying results. Sensitivity analyses suggested that in both cities, the mixed approach (interactive safer sex/didactic safer injection intervention) was highly cost-effective. The dual interactive approach was highly cost-effective in Ciudad Juarez but not in Tijuana.

This article illustrates the importance of targeting programmes that take into consideration city-level contexts. Although the cities are similar in many ways, the double interactive approach was not highly cost-effective in the Tijuana setting. This is likely to be due to the fact that needle syringe distribution at the community level expanded at the same time, making the interactive safer injection practice component redundant. This supports previous research that community-level programmes, such as needle-exchange programmes, could be potentially more cost-effective than individual-level activities. Individual-level activities may then be best suited for settings where needle-syringe programmes are not available, such as in prisons. 

Latin America [7]
Mexico [8]
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