1. Division of Occupational Medicine and Centre for Environmental & Occupational Health Research, School of Public Health and Family Medicine, University of Cape Town , Room 4. 45, Fourth Level, Falmouth Building Anzio Road, Observatory, 7925, Cape Town , South Africa
2. Department of Environmental and Occupational Health, School of Public Health and Social Sciences, Muhimbili University of Health and Allied Sciences , Dar es Salaam , Tanzania
3. Department of Environmental and Occupational Studies, Faculty of Applied Sciences, Cape Peninsula University of Technology , Cape Town , South Africa