[1] Childrens Natl Med Ctr, Child Hlth Advocacy Inst, Washington, DC 20010 USA
[2] George Washington Univ, Sch Med, Emergency Med & Prevent & Community Hlth, Washington, DC USA
[3] George Washington Univ, Sch Publ Hlth, Washington, DC USA
[4] Maryland Inst Emergency Med Serv Syst, Baltimore, MD 21201 USA