[1] Columbia Univ, Mailman Sch Publ Hlth, Dept Epidemiol, New York, NY 10032 USA
[2] New York Acad Med, Ctr Urban Epidemiol Studies, New York, NY USA
[3] Collaborat Inject Drug Users Study, CIDUS 2, Baltimore, MD USA
[4] Johns Hopkins Univ, Bloomberg Sch Publ Hlth, Dept Epidemiol, Infect Dis Program, Baltimore, MD USA
[5] Univ Maryland, Ctr Substance Abuse Res, College Pk, MD 20742 USA
[6] Johns Hopkins Univ, Bloomberg Sch Publ Hlth, Dept Mental Hyg, Baltimore, MD USA
[7] CDC, Natl Ctr HIV STD & TB Prevent, Div Std HIV Prevent, Atlanta, GA 30333 USA