I am a statistical epidemiologist, whose main research interest is in the epidemiology of infectious diseases of public health importance in low and middle income countries. I have a particular interest in the epidemiology and control of HIV and related infections, including sexually transmitted infections and tuberculosis. I have been one of the principal investigators of a collaborative programme of research in Mwanza, Tanzania whose aim is to develop and evaluate effective preventive interventions against the HIV epidemic, and helped to establish the Mwanza Intervention Trials Unit which aims to develop as an East African centre of excellence in this area. I am also involved in collaborative research on HIV and related infections in other parts of Africa, including Uganda, Zimbabwe, Zambia and South Africa. I am also involved in work on statistical and epidemiological methods and on transmission models of HIV and other STIs. I have a special interest in intervention trials and in particular have conducted research on the design and analysis of cluster-randomised trials. I am a senior member of the MRC International Statistics and Epidemiology Group (ISEG) and have jointly headed the Biostatistics Core of CREATE, a Gates-funded consortium to evaluate the impact of innovative TB control measures in HIV-endemic populations. I was principal investigator of the HPTN 071 (PopART) study, a cluster-randomised trial which evaluated the impact of a universal testing and treatment intervention on population-level HIV incidence in Zambia and South Africa.