1. Division of Epidemiology and Biostatistics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town 7500, South Africa
2. Department of Chemical Pathology, Faculty of Medicine and Health Sciences, Sefako Makgatho Health Sciences University, Pretoria 0208, South Africa
3. National Health Laboratory Service, Dr George Mukhari Academic Hospital, Pretoria 0208, South Africa
4. Department of Chemical Pathology, Faculty of Health Sciences, University of Pretoria, Pretoria 0028, South Africa
5. National Health Laboratory Service, Steve Biko Academic Hospital, Pretoria 0002, South Africa
6. Department of Statistics, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria 0028, South Africa
7. Division of Epidemiology and Biostatistics, School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2193, South Africa