[1] Le Bonheur Childrens Hosp, Div Pediat Emergency Med, Memphis, TN 38103 USA
[2] Univ Tennessee, Hlth Sci Ctr, Memphis, TN USA
[3] Univ Tennessee, Hlth Sci Ctr, Tennessee Clin & Translat Sci Inst, Memphis, TN USA
[4] Univ Tennessee, Dept Prevent Med, Div Epidemiol, Hlth Sci Ctr, Memphis, TN USA