作者单位:UCLA, David Geffen Sch Med, Dept Med, Los Angeles, CA USA[1]Cedars Sinai Med Ctr, Los Angeles, CA 90048 USA[2]Virginia Commonwealth Univ, Childrens Hosp Richmond, Richmond, VA 23284 USA[3]Univ Wisconsin Madison, Dept Pediat, 600 Highland Ave, Madison, WI 53792 USA[4]RAND Corp, RAND Hlth, Santa Monica, CA USA[5]