1. Imperial College Healthcare NHS Trust, London, W2 1NY, United Kingdom
2. Department of Health, London, SW1A 2NS, United Kingdom
3. Barnet and Chase Farm Hospitals NHS Trust, London, EN2 8JL, United Kingdom
4. WHO Patient Safety, World Health Organization, Geneva 27, Switzerland
5. NHS Tower Hamlets, London, E1 1RD, United Kingdom
6. Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland 21205;