H Hall1, C Cosgrove2,3, A Houston2, D C Macallan2,3, R Aul1. 1. From the Department of Respiratory Medicine. 2. Infection Care Group, St George's University Hospitals NHS Foundation Trust, SW17 0QT, London, UK. 3. Institute for Infection and Immunity, St George's University of London, SW17 0QT, London, UK.