1. London School of Economics and Political Science, Institute of Social Psychology, Houghton Street, London, UK
2. Biomedical Research and Training Institute, Manicaland Project, Harare, Zimbabwe
3. Department of Health Promotion and Development, University of Bergen, Bergen, Norway
4. Research Department of Infection & Population Health, Royal Free and UC Medical School, University College, London, UK
5. Infectious Disease Epidemiology, Imperial College, London, UK