1. Division of Epidemiology and Biostatistics School of Public Health and Family Medicine University of Cape Town Cape Town South Africa
2. Division of Maternal Fetal Medicine Department of Obstetrics and Gynaecology University of Cape Town Cape Town South Africa
3. Centre for Infectious Disease Epidemiology and Research School of Public Health and Family Medicine University of Cape Town Cape Town South Africa
4. School of Human Development and Health University of Southampton Southampton UK
5. School of Public Health University of the Witwatersrand Johannesburg South Africa