1. Acute Medicine Department, Ninewells Hospital and Medical School, Dundee, DD1 9SY, UK
2. The Infection Unit, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, AB25 2ZN, UK
3. Department of Medical Statistics, Department of General Practice and Primary Care, The University of Aberdeen, Foresterhill Health Centre, Westburn Road, Aberdeen AB25 2AY, UK