1. Department of Dermatology, University of Pennsylvania, Philadelphia, USA
2. Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania, Philadelphia, USA
3. Department of Medicine, Christiana Care Health Care System, Wilmington, USA
4. Department of Internal Medicine, University of Botswana, Gaborone, Botswana
5. Department of Dermatology, University of California, San Francisco, USA