[1] Northwestern Univ, Feinberg Sch Med, Dept Med, Div Rheumatol, Chicago, IL 60611 USA
[2] Univ Pittsburgh, Sch Med, Dept Med, Div Clin Immunol & Rheumatol, Pittsburgh, PA 15260 USA
[3] Univ Pittsburgh, Sch Publ Hlth, Dept Epidemiol, Pittsburgh, PA 15260 USA