[1] Duke Univ, Sch Med, Dept Surg, DUMC 3513, Durham, NC 27710 USA
[2] Duke Univ, Sch Med, Dept Populat Hlth Sci, Durham, NC USA
[3] Denver Hlth, Dept Emergency Med, Denver, CO USA
[4] Univ Colorado, Sch Med, Denver, CO USA
[5] Colorado Sch Publ Hlth, Dept Epidemiol, Aurora, CO USA
[6] Boston Univ, Sch Med, Dept Surg, Boston, MA 02118 USA
[7] Boston Med Ctr, Boston, MA USA