An estimated 1.2 million people live in Tijuana, with 57% between the ages of 15–49 years and 49% being women. Based on the high growth scenario, our data suggest that up to one in every 125 persons aged 15–49 years in Tijuana is HIV-infected. According to criteria established by UNAIDS/WHO, the state of the HIV epidemic in Tijuana has moved from low-level to concentrated and could become generalized if the HIV prevalence among sentinel populations is consistently above 1%.26
Our model suggests that transmission in high-risk groups, such as MSMs and IDUs, may be driving the HIV epidemic in Tijuana. However, there is substantial overlap between MSMs and IDUs in Tijuana. A study by Magis-Rodriguez et al. found that among a sample of 352 male IDUs in Tijuana, 48% reported having ever had sex with another male.20
Similarly, among 187 male IDUs recruited in Tijuana through respondent-driven sampling in 2005, 47% reported having ever had sex with another male (Strathdee et al. unpublished data). Since MSM who also inject drugs are known to have high HIV incidence in other settings,27,28
it is important to implement targeted interventions for both populations and subgroups of MSM-IDUs before a more generalized epidemic develops.
There is also concern that the number of HIV-infected women may rise in Tijuana. Our analyses suggest that the number of HIV-infected women in Tijuana between ages 15 and 49 may be as low as 498 or as high as 1,296. A qualitative study conducted in 2004 found that FSWs in Tijuana seldom negotiated the use of condoms, had a low knowledge regarding the proper use of condoms, and did not like to use condoms with clients because they were perceived as uncomfortable.29
An ongoing quantitative study among FSWs in Tijuana recently found that injection of vitamins and illicit drugs (e.g. methamphetamine, cocaine) was common among FSWs in Tijuana.21
The link between drug use and HIV in pregnant women in Tijuana further suggests that HIV could soon become more generalized in Tijuana unless immediate preventive actions are taken.3
Since the latter study was conducted, HIV antibody screening of pregnant women in Tijuana is now becoming routine, and provisions have been made for administering antiretrovirals to HIV-positive pregnant women.
Our model provides a snapshot of the current HIV situation in Tijuana; however, comparison with earlier figures suggests the situation is dynamic. While studies conducted in 1987 and 1988 found that HIV prevalence was 0.5–1% in FSWs,23,30
more recent surveys of HIV in this sub-population found prevalence near 5%.21
Further, while studies throughout the late 1980s and 1990s consistently found HIV prevalence to be less than 2% among IDUs,13,23
recent prevalence data range from 2.3 to 6.5%.20
A rise in HIV prevalence among IDUs in Tijuana is hardly surprising given that HCV prevalence is 96%,24
needle sharing and the use of shooting galleries are normative, there is no formal needle exchange program, and pharmacists often refuse to sell syringes to drug users despite its legality.31
Theses changes in HIV prevalence over time indicate that there is a need to study the temporal trend of HIV incidence in order to make future projections that inform health policy planning efforts.
The current estimates of HIV prevalence in Tijuana suggest the need for expanding HIV prevention and treatment efforts and developing culturally appropriate interventions for high-risk populations in the Mexico–U.S. border region. Despite Mexico's policy of providing ‘universal coverage’ for antiretrovirals, supplies are commonly inadequate and sporadic, and there is a lack of specialized medical providers. A recent survey of IDUs found that only half had ever had an HIV test.20
The mobility of the Tijuana population is also of concern for identifying and treating persons with HIV infection. A recent survey of 116 HIV positive residents in Tijuana found that 64% crossed the border to the U.S. at least once per month in the past year.32
This has implications for preventing HIV transmission as well as logistical issues in providing medical care to patients.
Any model is only as valid as the data it incorporates. Our work was limited in that there is a dearth of reliable data on HIV incidence and prevalence in Tijuana. For this reason, we incorporated data from a variety of reliable sources to create a likely range of the true HIV prevalence estimate for each subpopulation. Although we made an effort to include known risk groups, it is possible that our model lacks data on unknown risk groups. Further, we did not include data on prisoners, which has been found to be a population at high risk for HIV infection.17,33
Past studies have shown that nearly 100% of HIV-infected prisoners are also IDUs; therefore, we intentionally omitted this group to avoid the possibility of double-counting. This may have led to an underestimation of the number of HIV cases due to drug use in the city. On the other hand, there is a substantial overlap between MSM and IDU populations in Tijuana, and as we included both of these groups in the model, this may have led to an overestimation of HIV cases.
The prevalence of HIV in Tijuana is likely also affected to some extent by migrant workers.22
As many persons pass through Tijuana en route to the U.S. or other parts of Mexico, migration may have implications both on the introduction of new HIV infections to the city, as well as dissemination of HIV to other parts of the U.S. and Mexico. However, as there are no reliable estimates of the number and duration of stay of such migrants and in particular of those migrants who inject drugs, are MSM or are female or male sex workers or their clients, we did not include migrants in our model. The underlying population structure of our model was based on the most recent general census of Tijuana, conducted in 2000.2
As the city has been growing at a rate of approximately 5% per year, it is likely that the current number of HIV positive persons in the city is higher than our estimates.
The greatest uncertainty in the model was in the estimates of subgroup populations. To our knowledge, there are no firm estimates of the number of MSM in Mexico; if the proportion of all adult males who engage in sex with other males is greater than 5%, our estimates of HIV positive MSM in Tijuana may be grossly underestimated. Since injection drug use is an illegal activity, there are no valid estimates of the number of IDUs in Tijuana; however, it has long been recognized that Tijuana has the most serious drug abuse problem in Mexico. While we can be fairly confident about the number of registered FSW in Tijuana, since this is a municipal requirement, the number of unregistered FSWs, who are likely to engage in higher risk behaviors, is less reliable.
Despite the limitations of our models, even the low growth scenario suggests that HIV/AIDS should be considered a public health priority along the Mexico–U.S. border. Our study indicates that nationwide statistics of HIV/AIDS in Mexico mask a dynamic sub-epidemic along the Mexico–U.S. border, whereby “pockets” of HIV infection likely exist among subgroups of IDUs, MSM and sex trade workers in Tijuana. Our modeling scenario, accounting for current HIV prevalence estimates, indicates that up to one in 125 persons aged 15–49 years in Tijuana may be infected with HIV. In addition to the need to develop culturally appropriate interventions targeted to MSMs, IDUs and other at-risk groups, expansion of free HIV voluntary testing and counseling is needed. As Tijuana is situated on the busiest land border crossing in the world, evidence of high-risk behaviors and rising HIV prevalence has important implications for both Mexico and the U.S.