1. Public Health England Primary Care Unit, Microbiology Department, Gloucester Royal Hospital, Gloucester, UK
2. Centre for Dental Public Health and Primary Care, Institute of Dentistry, Bart’s and The London School of Medicine & Dentistry, Queen Mary, University of London, London, UK
3. Barts Health NHS Trust, Whitechapel, London, UK
4. Department of Biostatistics, University of Liverpool, Liverpool, UK