[1] UCL, Dept Med, Ctr Rheumatol, Bloomsbury Rheumatol Unit, London W1P 9PG, England
[2] McGill Univ, Montreal Gen Hosp, Div Clin Immunol Allergy, Montreal, PQ H3G 1A4, Canada
[3] McGill Univ, Montreal Gen Hosp, Div Clin Epidemiol, Montreal, PQ H3G 1A4, Canada
[4] Univ London, London Sch Hyg & Trop Med, Med Stat Unit, London, England