[1] Natl Univ Singapore, Yong Loo Lin Sch Med, Dept Paediat, Singapore 119074, Singapore
[2] Minist Hlth, Epidemiol & Dis Control Div, Singapore, Singapore
[3] Univ Melbourne, Sch Med, Melbourne, Vic, Australia
[4] Univ Western Australia, Sch Paediat & Child Hlth, Perth, WA 6009, Australia
[5] Univ Hong Kong, Queen Mary Hosp, Dept Paediat & Adolescent Med, Hong Kong, Hong Kong, Peoples R China
[6] Kwong Wah Hosp, Dept Paediat, Hong Kong, Hong Kong, Peoples R China