Background:  The California-Mexico Epidemiological Surveillance Pilot (CMESP) is a bi-national collaboration project with the goal of assessing HIV and sexually transmitted infection (STI) prevalence, vulnerabilities, risk behaviors, and other associated factors among Mexican migrants at selected venues in 2 counties in California. 

Methods:  The CMESP is a venue-based targeted random sampling of male and female Mexican migrants living in rural and urban areas in the counties of San Diego and Fresno using a 35-minute survey instrument and collection of blood and urine specimens for HIV and STI testing. Participants were systematically sampled and recruited at each venue in proportion to the volume of eligible migrants enumerated at that venue, with over-sampling of high-risk venues. The  HIV and STI unweighted prevalence is estimated separately for participants recruited from either general living- or work-related venues, including migrant camps, job pick-up locations, laundromats, parks, and churches; or traditional high-risk venues including bars and night clubs. 

Results:  A total of 1296 Mexican migrants were surveyed at 68 venues in 2004 and 2005, including 1009 at 56 living- or work-related venues and 287 at 12 high-risk venues.  The prevalence of HIV was 0.1% at living- or work-related venues, and 1.8% at high-risk venues. No HIV was found among women. The prevalence of syphilis, 1.0% at living- or work-related venues and 2.45% at high-risk venues; Chlamydia trachomatis, 2.7% at living- or work-related venues, and 3.5% at high-risk venues; hepatitis B (measured by core antibody) 5.2% at living- or work-related venues, and 5.9% at high-risk venues; hepatitis C 2.1% at living- or work-related venues, and 1.7% at high-risk venues. The 1001 male participants reported the following behaviors in the past 12 months:  men who have sex with men (MSM), 2.1% at living- or work-related venues, 45.3% at high-risk venues (at high-risk venues, 56.9%, of these MSM also reported sex with women); exchanged money for sexual favors, 14.9% at living- or work-related venues, 19.3% at high-risk venues; no condom used at last sex with a sex worker, 19.7% at living- or work-related venues, 40% at high-risk venues; used cocaine or methamphetamine, 19.4% at living- or work-related venues, 25.6% at high-risk venues.

Conclusions:  These data suggest that Mexican migrants are at risk for HIV, STI, and hepatitis infections while in California. Preliminary results raise concerns that the HIV and STI epidemics may expand more aggressively among this population in the future. These results have implications for tailored prevention interventions in Mexican migrant communities in California and elsewhere.