[1] Univ Calif San Francisco, Dept Med, Div Geriatr, 3333 Calif St,Suite 380, San Francisco, CA 94118 USA
[2] Univ Calif Berkeley, Sch Publ Hlth, Epidemiol Div, Berkeley, CA 94720 USA
[3] Univ Calif San Francisco, Ctr AIDS Prevent Studies, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Prevent Res Ctr, San Francisco, CA 94143 USA