[1] Harvard Univ, Sch Med, Div Cardiovasc Med, Brigham & Womens Hosp, Cambridge, MA 02138 USA
[2] Harvard Univ, Sch Publ Hlth, Dept Hlth Policy & Management, Cambridge, MA 02138 USA
[3] Univ Cape Town, ZA-7700 Rondebosch, South Africa
[4] Brigham & Womens Hosp, Div Gen Med, Boston, MA 02115 USA
[5] Harvard Univ, Sch Med, Dept Hlth Care Policy, Cambridge, MA 02138 USA
[6] Harvard Univ, Sch Publ Hlth, Dept Global Hlth & Populat, Cambridge, MA 02138 USA