[1] Menzies Sch Hlth Res, Child Hlth Div, Casuarina, Australia
[2] Univ Nottingham, Div Epidemiol & Publ Hlth, Nottingham, England
[3] Royal Darwin Hosp, Dept Resp Med, Darwin, NT, Australia
[4] Prince Charles Hosp, Thorac Programme, Chermside, Australia
[5] Univ Melbourne, Melbourne Sch Populat & Global Hlth, Ctr Epidemiol & Biostat, Allergy & Lung Hlth Unit, Melbourne, Vic, Australia