1Respiratory Unit, Morriston Hospital, Heol Maes Eglwys, Swansea, SA6 6NL, UK
2Department of Respiratory Medicine, Llandough Hospital, Penlan Road, Cardiff, CF64 2XX, UK
3Common Cold Centre, Cardiff School of Biosciences, Cardiff University, Cardiff, CF10 3AX, UK
4School of Medicine, Swansea University, Swansea SA2 8PP, UK