1. Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong, China
2. Centre for Epidemiology Versus Arthritis, The University of Manchester, Manchester M139PT, UK
3. Department of Statistics, The Chinese University of Hong Kong, Hong Kong, China
4. Department of Medicine, Queen Mary Hospital, Hong Kong, China
5. Department of Microbiology and Carol Yu Centre for Infection, The University of Hong Kong, Queen Mary Hospital, Hong Kong, China