[1] Harvard Univ, Sch Publ Hlth, Dept Environm Hlth, Boston, MA 02130 USA
[2] Univ N Carolina, Sch Publ Hlth, Dept Epidemiol, Chapel Hill, NC USA
[3] Ctr Dis Control & Prevent, Div Sci Lab, Natl Ctr Environm Hlth, Atlanta, GA USA
[4] Cincinnati Childrens Hosp, Med Ctr, Dept Pediat, Cincinnati, OH USA
[5] Univ Cincinnati, Coll Med, Dept Environm Hlth, Cincinnati, OH 45267 USA
[6] Simon Fraser Univ, Child & Family Res Inst, British Columbia Childrens Hosp, Vancouver, BC, Canada
[7] Simon Fraser Univ, Fac Hlth Sci, Vancouver, BC, Canada