[1] Univ Newcastle, Ctr Asthma & Resp Dis, Dept Resp & Sleep Med, John Hunter Hosp, New Lambton, NSW 2305, Australia
[2] John Hunter Childrens Hosp, Dept Resp Med, New Lambton, NSW, Australia
[3] Univ Newcastle, Sch Med & Publ Hlth, Newcastle, NSW 2300, Australia
[4] Univ Newcastle, Sch Nursing & Midwifery, Newcastle, NSW 2300, Australia
[5] Univ Newcastle, Ctr Asthma & Resp Dis, Newcastle, NSW 2300, Australia
[6] Hunter Med Res Inst Resp & Sleep Med, Newcastle, NSW, Australia