[1] Umea Univ, Clin Sci, Pediat, Umea, Sweden
[2] Solleftea Hosp, Dept Pediat, SE-88133 Solleftea, Sweden
[3] Karolinska Inst, Orebro Cty Council, Child Hlth Care Unit, Stockholm, Sweden
[4] Karolinska Inst, Dept Publ Hlth Sci, Div Social Med, Stockholm, Sweden
[5] Karolinska Inst, Dept Med Epidemiol & Biostat, Stockholm, Sweden
[6] Umea Univ, Occupat & Environm Med, Umea, Sweden
[7] Vasternorrland Cty Council, Dept Res & Dev, Umea, Sweden