[1] Univ Bergen, Dept Publ Hlth & Primary Hlth Care, Bergen, Norway
[2] Univ Ferrara, Neurol Clin, I-44100 Ferrara, Italy
[3] Univ Sassari, Neurol Clin, I-07100 Sassari, Italy
[4] Clin Ctr Serbia, Inst Neurol, Belgrade, Serbia
[5] Univ Oslo, Rikshosp, Inst Immunol, Radium Hosp,Med Ctr, N-0027 Oslo, Norway
[6] Linkoping Univ, Dept Clin Neurol, Linkoping, Sweden
[7] Haukeland Hosp, Dept Neurol, N-5021 Bergen, Norway
[8] Univ Belgrade, Dept Epidemiol, Belgrade, Serbia
[9] McGill Univ, Dept Epidemiol & Biostat, Montreal, PQ, Canada