[1] Johns Hopkins Univ, Dept Med, Div Gen Internal Med, Baltimore, MD 21218 USA
[2] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Epidemiol, Baltimore, MD USA
[3] Johns Hopkins Bloomberg Sch Publ Hlth, Welch Ctr Prevent Epidemiol & Clin Res, Baltimore, MD USA
[4] Univ Minnesota, Sch Med, Dept Lab Med & Pathol, Minneapolis, MN 55455 USA