Participants and Procedures

Estimates of engagement in the HIV care continuum were drawn from six epidemiologic studies conducted among key populations disproportionately affected by HIV in Tijuana (see Table I). Participant recruitment and baseline HIV testing protocols were complete for all six studies at time of analysis. Follow-up data from one study (El Cuete IV) is ongoing; this analysis includes data collected through December 11, 2013. Each study was selected because it used: 1) sampling methods to estimate HIV prevalence in its respective target population, 2) conducted HIV testing as part of study participation, and 3) had obtained survey data from HIV-positive participants documenting any previous HIV testing and treatment histories. This resulted in a pooled sample of 3,368 participants who were tested for HIV and surveyed on HIV-related risk factors. While most of these studies excluded participants if they were enrolled in another HIV study; it may be possible that a few individuals were sampled across more than one study.

Pooled Sample and Individual Study Characteristics

RCT (Randomized Controlled Trial), RDS (Respondent-driven Sampling), Confirmatory HIV testing protocols: IFA (immunofluorescence assay), EIA (HIV-1 enzyme immunoassay).

Study methods for these individual studies have either previously been published or are currently under review.(6,25–28) In brief, across all studies, eligible participants were required to be ≥18 years of age and meet the studies’ target population requirements: Proyecto H enrolled biologically male participants who had engaged in sex with another man in the past 2 months.(6) El Cuete III and El Cuete IV enrolled PWID who reported having injected illicit drugs in the past month, confirmed by injection stigmata (i.e., track marks).(25,26) Mujer Segura enrolled biologically female participants who had engaged in condom-unprotected sex work (SW) with ≥1 male client in the past 2 months.(27) Mujer Mas Segura enrolled biologically female participants who reported both condom-unprotected sex work with ≥1 male client and sharing drug injection equipment in the past month.(28) In Salud Fronteriza, all patients accessing free primary care services at the HFiT clinic were sequentially asked to participate in their survey and HIV testing protocol; participants generally reflect the Zona Norte community, a primarily indigent and low-resourced population affected by migration and deportation.

For each study, data collection was interviewer-administered in English or Spanish based on participants’ preference using computer-assisted personal interviewing (CAPI) or similar tablet-based surveys; except Proyecto H which was administered via paper and pencil. HIV and confirmatory testing protocols varied, but were adherent to the most current national, US (CDC) and Mexico (CENSIDA), or international, WHO, testing recommendations during their respective study periods. All participants provided informed consent and were compensated for their time. Participants who refused HIV testing as part of study participation were excluded from the current analysis. Each study obtained human subjects approval from the University of California, San Diego and respective institutions in Mexico.