Study participants were from the UHS, a serial, cross-sectional, sero-epidemiological study of IDUs in the San Francisco Bay Area from 1986 to 2005.[16,17] Study eligibility criteria included injection of an illicit drug in the past 30 days (verified by signs of venipuncture), ability to provide informed consent, age 18 or older, and ability to speak English or Spanish. Participants were interviewed face-to-face regarding key demographics, drug use, and sexual risk behavior. HIV-1 infection status was determined from serum blood samples using enzyme immunoassay and Western Blot assay, identifying HIV+ cases as those who had detectable antibodies.[16,17] The present analysis included self-reported Caucasians (henceforth referred to as European Americans [EAs]) and African Americans (AAs).
