[1] RTI Int, Waltham, MA 02451 USA
[2] E Carolina Univ, Brody Sch Med, Dept Pediat, Greenville, NC 27834 USA
[3] E Carolina Univ, Brody Sch Med, Dept Publ Hlth, Greenville, NC 27834 USA
[4] Ann & Robert H Lurie Childrens Hosp Chicago, Res Ctr, Mary Ann & J Milburn Smith Child Hlth Res Program, Pediat Practice Res Grp, Chicago, IL 60611 USA
[5] RTI Int, Res Triangle Pk, NC 27709 USA
[6] NHLBI, Bethesda, MD 20892 USA