1. Respiratory and Systemic Infection Laboratory, Health Protection Agency, Microbiology Services Division, Colindale, London, UK
2. Department of Bioanalysis and Horizon Technologies, Health Protection Agency, Microbiology Services Division, Colindale, London, UK
3. Applied Bioinformatics Laboratory & Epidemiology, Health Protection Agency, Microbiology Services Division, Colindale, London, UK
4. Statistics, Modelling and Economics Department, Health Protection Agency, Microbiology Services Division, Colindale, London, UK