[1] Duke Univ, Dept Med, Div Gen Internal Med, Sch Med, 200 Morris St,3rd Fl, Durham, NC 27701 USA
[2] Johns Hopkins Bloomberg Sch Publ Hlth, Welch Ctr Prevent Epidemiol & Clin Res, Dept Epidemiol, Baltimore, MD USA
[3] Johns Hopkins Bloomberg Sch Publ Hlth, Welch Ctr Prevent Epidemiol & Clin Res, Gen Internal Med & Phys Med & Rehabil, Baltimore, MD USA
[4] Univ Calif San Francisco, Sch Med, San Francisco, CA USA