1. School of Health Systems and Public health, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa
2. Department of Public Health, School of Nursing and Public health, Faculty of Health Sciences and Veterinary Medicine, University of Namibia, Oshakati, Namibia
3. Department of Occupational and Environmental Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
4. Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden