[1] Boston Med Ctr, Gen Internal Med Sect, Boston, MA USA
[2] Boston Univ, Sch Med, Boston, MA 02118 USA
[3] Cambridge Hlth Alliance, Dept Med, Cambridge, MA USA
[4] Harvard Univ, Sch Med, Cambridge, MA 02138 USA
[5] Ctr Dis Control & Prevent, Atlanta, GA USA
[6] Cambridge Hlth Alliance, Dept Community Affairs, Cambridge, MA USA
[7] Cambridge Hlth Alliance, Dept Gastroenterol, Cambridge, MA USA
[8] Harvard Univ, Sch Med, Dept Ambulatory Care & Prevent, Boston, MA USA
[9] Harvard Pilgrim Hlth Care, Boston, MA USA
[10] Harvard Univ, Sch Publ Hlth, Dana Farber Canc Inst, Boston, MA 02115 USA
[11] Brigham & Womens Hosp, Div Gen Med, Boston, MA 02115 USA
[12] Harvard Univ, Sch Med, Boston, MA USA