Ahmed Ali1, Omar Musbahi2, Veronica L C White3, Alexander Sheriff Montgomery3. 1. Bart's and The London School of Medicine and Dentistry, Queen Mary University of London, London, England. 2. Oxford University Clinical Academic Graduate School, Oxford University, Oxford, England. 3. Department of Respiratory Medicine and Infectious Diseases (V.L.C.W.) and Spinal Department (A.S.M.), Royal London Hospital, London, England.