[1] Univ Fed Pelotas, Postgrad Program Epidemiol, Rua Marechal Deodoro 1160,3 Andar, BR-96020220 Pelotas, RS, Brazil
[2] Brazilian Minist Hlth, Nossa Senhora Conceicao Childrens Hosp, Porto Alegre, RS, Brazil
[3] Univ Sao Paulo, Dept Med Prevent, Sao Paulo, Brazil
[4] Univ Toronto, Hosp Sick Children, Res Inst, Dept Paediat, Toronto, ON, Canada