[1] Imperial Coll London, Sch Publ Hlth, Dept Primary Care & Publ Hlth, London, England
[2] Univ Naples Federico II, Dept Publ Hlth, Naples, Italy
[3] Univ Manitoba, Max Rady Coll Med, Rady Fac Hlth Sci, Dept Med & Community Hlth Sci, Winnipeg, MB, Canada
[4] UCL, UCL Queen Sq Inst Neurol, Fac Brain Sci, Queen Sq Multiple Sclerosis Ctr,Dept Neuroinflamma, London, England
[5] Univ Coll London Hosp, Natl Inst Hlth Res, Biomed Res Ctr, London, England
[6] Imperial Coll London, Sch Publ Hlth, Dept Primary Care & Publ Hlth, London W6 8RP, England