1. Department of General Practice and Primary Care, St George's Hospital Medical School, Cranmer Terrace, London SW17 ORE, U.K.
2. Department of Medicine, St George's Hospital Medical School, Cranmer Terrace, London SW17 ORE, U.K.
3. Department of Clinical and Experimental Medicine, Federico II Medical School, Naples, Italy
4. Department of Public Health Sciences, St George's Hospital Medical School, Cranmer Terrace, London SW17 ORE, U.K.