[1] Tufts Univ, Sch Med, Dept Community Hlth, Nutr Unit, Boston, MA 02111 USA
[2] Tufts Univ, Sch Med, Tupper Res Inst, Div Geog Med & Infect Dis, Boston, MA 02111 USA
[3] Tufts Univ, Sch Med, Dept Med, Boston, MA 02111 USA
[4] Tufts Univ, New England Med Ctr Hosp, Boston, MA 02111 USA
[5] Harvard Univ, Sch Publ Hlth, Dept Epidemiol, Boston, MA 02115 USA
[6] Harvard Univ, Sch Publ Hlth, Dept Biostat, Boston, MA 02115 USA