Background:  Researchers have hypothesized that the effect of migration from Mexico to the United States leads to increased risk for HIV infection. Previous studies have identified an association between migration and HIV high-risk behaviors; however, the more important question of causation has not been addressed. Utilizing a crossover study design, we collected data to directly assess the causal effect of migration on HIV high-risk behaviors among Mexican migrants.

Methods:  The California-Mexico Epidemiological Surveillance Pilot, a binational collaboration, combines targeted, venue-based sampling, outreach techniques, and survey methods to estimate HIV high-risk behavior. In 2005, we redesigned the survey to collect new data that would allow us to assess the effect of migration. We collected data on HIV high-risk behaviors prior to and after migration, creating matched-pair data for each subject. The strength of this crossover design is that each person serves as his own control. Using exact conditional logistic regression, we estimated odds ratios with 95% confidence intervals, controlling for venue type and gender.

Results:  We sampled 458 Mexican migrants from male work and community venues, bars, and clubs in rural and urban sites in Fresno and San Diego County in California. Results show a significant decrease after migration in the number of males reporting low condom use and sharing needles. However, there is a significant increase after migration in the number of males adopting HIV high-risk behaviors related to sex with a sex worker, sex work, and sex while under the influence of drugs or alcohol.

*Mid-p value

Conclusions:  Migration's significant effect on increased HIV high-risk behaviors among male Mexican migrants, specifically, suggests that, without intervention, the HIV epidemic may expand among this population. These results suggest targeting prevention interventions to those venues where this hard-to-reach population is concentrated.