Morar R
Department of Pulmonology and Critical Care, Charlotte Maxeke Johannesburg Academic Hospital and University of the Witwatersrand, South Africa
Richards GA
Department of Pulmonology and Critical Care, Charlotte Maxeke Johannesburg Academic Hospital and University of the Witwatersrand, South Africa
Murray J
National Institute of Occupational Health of the National Health Laboratory Services and Faculty of Public Health, University of the Witwatersrand, South Africa