1. Global Health Research ProgramThe University of British Columbia (UBC), Vancouver, BC, Canada
2. Provincial Occupational Health Unit, Free State Department of Health, University of the Free State, Bloemfontein, South Africa
3. National Institute for Occupational HealthA Division of the National Health Laboratory Service, Johannesburg, South Africa
4. School of Health Systems and Public HealthUniversity of Pretoria, Pretoria, South Africa