Background: Young injection drug users (IDU) are highly mobile. It is not known how mobility affects their risk of acquiring and transmitting viral infections. Methods:We conducted a cross-sectional study of young (under age 30) IDU in San Francisco (2004)(2005)(2006). Participants completed a semi-structured interview and testing for hepatitis B virus (HBV), hepatitis C virus (HCV) and HIV infection. We examined whether travel was independently associated with drug, alcohol, sexual risk behaviors, and infection status, after adjusting for demographic characteristics and years injecting.Results: Two-thirds (62%) reported past (3 months) travel outside of San Francisco (n=355). Travelers, as compared to non-travelers, were more likely to be under age 20, female, and planned to leave San Francisco in the coming months. Travel was independently associated with heavy alcohol consumption, drinking alcohol until blackout, poly-substance use, more sexual and injecting partners, and receptive needle/syringe sharing, sharing drug preparation equipment, backloading syringes, and pooling money to buy drugs. In an analysis of interactions with travel, younger travelers were more likely to be HCV positive than younger non-travelers.Discussion: Traveling young IDU are at exceptionally high risk for acquiring and transmitting viral infections, while their mobility makes it challenging to effectively deliver interventions.

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