Reduced Infectious Disease Risk among Recent Border Crossing Injection Drug Users along the Mexico/U.S. Border

Illicit drug use in Mexico is concentrated along the Mexico/U.S. border. San Diego/Tijuana is the busiest land border crossing in the western hemisphere. We sought to characterize behaviors of injection drug users (IDUs) who were recent border crossers. From 4/06-6/07, Tijuana IDUs who injected within the last month were recruited using respondent-driven sampling, administered a survey, and tested for infectious diseases. Logistic regression compared IDUs who crossed to the U.S. in the past year with non-crossers. Of 1056 IDUs, 78% had ever traveled to the U.S., 7% in the past year, with 6% accessing U.S. health services. Half of recent border crossers worked, 21% bought and 4% sold drugs, 10% bought syringes, and 6% bought and 4% sold sex. Recent crossers were more likely to have injected with a U.S. resident (67% vs. 46%) and used drugs in the U.S. (80% vs. 56%). Independent associations with recent crossing were: being female (adjusted odds ratio (AOR)=2.23;95%CI=1.17-4.25); younger (AOR=0.95/year;95%CI:0.92-0.99); and completing secondary school (AOR=2.35;95%CI=1.35-4.11). Crossers had marginally lower prevalence of tuberculosis and HIV, and significantly lower syphilis (AOR=0.10;95%CI=0.02-0.42) and shooting gallery use (16% vs .40%). Although income was similar, recent crossers had higher odds of having someone from whom they could ask advice/borrow cash (2.13;95%CI=1.25-3.61), recent drug treatment (AOR=2.11;95%CI=1.03-4.34), and having family who used illicit drugs (AOR=1.81;95%CI=1.07-3.08). Cross-border interactions are common in Tijuana IDUs, suggesting potential for infectious disease spread, but also prevention and treatment services exposure. Cross-border health programs, investigations of U.S. IDUs cross-border activities, and prospective studies should be expanded.