[1] Univ N Carolina, Injury Prevent Res Ctr, Chapel Hill, NC 27599 USA
[2] Univ N Carolina, Dept Hlth Behav & Hlth Educ, Sch Publ Hlth, Chapel Hill, NC USA
[3] Univ N Carolina, Dept Epidemiol, Sch Publ Hlth, Chapel Hill, NC 27599 USA
[4] Univ N Carolina, Sch Publ Hlth, Dept Biostat, Chapel Hill, NC 27599 USA
[5] Univ N Carolina, Sch Med, Dept Pediat, Chapel Hill, NC 27599 USA
[6] Univ N Carolina, Sch Med, Dept Internal Med, Chapel Hill, NC 27599 USA
[7] Univ N Carolina, Sch Med, Dept Emergency Med, Chapel Hill, NC 27599 USA