[1] Oxford Univ Hosp NHS Trust, Oxford Ctr Resp Med, Oxford, England
[2] Univ Oxford, Churchill Hosp, Resp Trials Unit, Oxford, England
[3] Buckinghamshire Hosp NHS Trust, Dept Resp Med, Aylesbury, Bucks, England
[4] Royal Berkshire NHS Fdn Trust, Dept Resp Med, Reading, Berks, England
[5] Univ Oxford, NIHR Oxford Biomed Res Ctr, Oxford, England