[1] Johns Hopkins Univ, Sch Med, Div Gen Internal Med, Baltimore, MD 21287 USA
[2] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Epidemiol, Baltimore, MD USA
[3] Univ Mississippi, Sch Med, Jackson, MS 39216 USA
[4] Johns Hopkins Univ, Sch Med, Div Cardiol, Baltimore, MD USA