1. Occupational and Environmental Medicine, School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy University of Gothenburg Gothenburg Sweden
2. Department of Occupational and Environmental Medicine Sahlgrenska University Hospital Gothenburg Sweden
3. Discipline of Occupational and Environmental Health University of KwaZulu‐Natal Durban South Africa
4. Department of Medicine, Division of Occupational and Environmental Medicine University of California San Francisco California USA