[1] Wayne State Univ, Dept Pediat, Detroit, MI 48202 USA
[2] RTI Int, StatEpi Div, Res Triangle Pk, NC USA
[3] Eunice Kennedy Shriver Natl Inst Child Hlth & Hum, Bethesda, MD USA
[4] Univ Iowa, Dept Pediat, Iowa City, IA 52242 USA
[5] Emory Univ, Sch Med, Dept Pediat, Atlanta, GA USA
[6] Brown Univ, Dept Pediat, Providence, RI 02912 USA
[7] Case Western Reserve Univ, Dept Pediat, Cleveland, OH 44106 USA