1. Epidemiology Branch A3-05, NIEHS, PO Box 12233, Durham, NC 27709, USA.
2. Epidemiology Branch, National Institute of Environmental Health Sciences, Durham, North Carolina, USA
3. Division of Rheumatology, East Carolina University School of Medicine, Greenville, North Carolina, USA
4. Division of Rheumatology, Allergy, and Clinical Immunology, Duke University Medical Center, Durham, North Carolina, USA
5. Medical Research Service, Ralph H Johnson Veterans Administration Medical Center and the Medical University of South Carolina, Charleston, South Carolina, USA
6. Division of Rheumatology, Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
7. Division of Rheumatology and Immunology, Thurston Arthritis Research Center, University of North Carolina, Chapel Hill, North Carolina, USA