1. Department of Environmental Health, Faculty of Health Sciences, Doornfontein Campus, University of Johannesburg, Johannesburg 2094, South Africa
2. Department of Environmental Health, Faculty of Sciences, Pretoria Campus, Tshwane University of Technology, Pretoria 0183, South Africa
3. Environment and Health Research Unit, South African Medical Research Council, Johannesburg 2094, South Africa
4. Faculty of Health Sciences, School of Health Systems and Public Health, University of Pretoria, Pretoria 0001, South Africa