Characterization of People Living with HIV Who Inject Drugs in Mexico City: Importance for Transmission and Detection.

People who inject drugs (PWID) face a heightened risk of acquiring/transmitting HIV, enhanced by stigma and limited health care access. In Mexico, studies on PWID have focused on the north of the country. This study aimed to delineate characteristics of PWID living with HIV in Mexico City, identify profiles based on the substance injected, and evaluate variables associated with forming transmission clusters. A cross-sectional study was conducted with data from 2019 to 2023. Participants completed a questionnaire on sociodemographic, clinical, and behavioral variables. Bivariate and multi-variate logistic regression analyses were made. Among PWID, 96.3% were male ( n = 437), of which 90.1% were men who have sex with men, 1.5% were cisgender females ( n = 7), and 2.2% were transgender females ( n = 10). PWID were more likely to use drugs during sex (adjusted odds ratio [aOR] = 3.3, 95% confidence interval [CI]: 1.7-6.4, p < 0.001), have more sexually transmitted diseases (aOR = 1.7, 95% CI: 1.1-2.9, p = 0.035), and have less condom use (aOR = 0.5, 95% CI: 0.3-0.8, p = 0.002). The most frequently injected substance was crystal meth, and those who injected it were more likely to have syphilis (aOR = 2.9, 95% CI: 1.2-7.1, p = 0.021), use Grindr (aOR = 3.6, 95% CI: 1.5-8.9, p < 0.001), and engage in high-risk practices (aOR = 6.9, 95% CI: 2.1-22.7, p < 0.001) in the last 3 months. Those under 25 years ( p = 0.002), recently infected ( p < 0.001), and who practiced insertive anal sex ( p < 0.001) were more likely to be part of a cluster. These findings, and the increasing use of crystal meth, underscore the critical need to implement targeted risk-reduction strategies for PWID living with HIV and to design interventions responsive to specific profiles associated with different substances, taking into account not only their risk practices but also protective behaviors such as HIV testing.