[1] Univ North Carolina Chapel Hill, UNC Sch Med, Dept Pediat, Chapel Hill, NC USA
[2] Univ North Carolina Chapel Hill, Lineberger Comprehens Canc Ctr, Chapel Hill, NC USA
[3] Univ North Carolina Chapel Hill, Gillings Sch Global Publ Hlth, Dept Biostat, Chapel Hill, NC USA
[4] Natl Inst Environm Hlth Sci, Epidemiol Branch, Durham, NC USA
[5] Campbell Univ, Coll Pharm & Hlth Sci, Buies Creek, NC USA
[6] Campus Box 7236,170 Manning Dr,1185A Phys Off Bldg, Chapel Hill, NC 27599 USA